This morning, a Virgin Atantin 747 Jumbo Jet became the first commercial airplane to fly on biofuel. The short flight from London to Amsterdam used a blend of 20% babassu  oil mixed with 80% conventional jet fuel. What was really exciting about the flight was the fact that the engine did not have to be altered in any way for the biofuel to work While this is a great initial step in trying to reduce CO2(carbon-dioxide)emissions from airplanes. there are a lot of hurdles  that still need to be overcome. First and foremost, unlike the normal fuel used to run airplanes (known as Jet A),biofuel freezes at high altitudes. Also, Jet'A'fuel burns consistently (at the same pace),which means it provides a safe and reliable fuel for long flights--engineers are not sure if biofuel will be able to do the same. The biggest hurdle to a full biofuel switch is our ability to be able to grow enough crops that can be converted to biofuel. There are two concerns that scientists have in this matter - the first is that the land to grow the extra crops will come from clearing more of our forests and the second is that since it competes with what we eat, the price of food will go up. However, Richard Branson of Virgin Airlines, envisions that if biofuel starts to replace oil on a greater basis, it will be manufactured from algae produced in sewage treatment plants, not from food sources. Birgin Airlines is not the only one trying to look for alternative fuel sources. Earlier this year, an Airbus A380 used another alternative fuel-a man-made mix of gas-to-liquid, in one of its four engines. The flight was tested by Rolls Royce (manufacturer of jet engines), in partnership with Shell (an oil company). Rolls Royce is also working with Air New Zealand on a similar project. While a complete switch to alternative fuel may take years, it is very encouraging to see airlines, oil companies and airplane manufacturers all coming together to try to make it happen! .One of the hurdles to be overcome for a full biofuel switch is to  _  .
alter the engine for airplanes make biofuel burn consistently open more land to grow more crops develop sewage treatment plants
Question: This morning, a Virgin Atantin 747 Jumbo Jet became the first commercial airplane to fly on biofuel. The short flight from London to Amsterdam used a blend of 20% babassu  oil mixed with 80% conventional jet fuel. What was really exciting about the flight was the fact that the engine did not have to be altered in any way for the biofuel to work While this is a great initial step in trying to reduce CO2(carbon-dioxide)emissions from airplanes. there are a lot of hurdles  that still need to be overcome. First and foremost, unlike the normal fuel used to run airplanes (known as Jet A),biofuel freezes at high altitudes. Also, Jet'A'fuel burns consistently (at the same pace),which means it provides a safe and reliable fuel for long flights--engineers are not sure if biofuel will be able to do the same. The biggest hurdle to a full biofuel switch is our ability to be able to grow enough crops that can be converted to biofuel. There are two concerns that scientists have in this matter - the first is that the land to grow the extra crops will come from clearing more of our forests and the second is that since it competes with what we eat, the price of food will go up. However, Richard Branson of Virgin Airlines, envisions that if biofuel starts to replace oil on a greater basis, it will be manufactured from algae produced in sewage treatment plants, not from food sources. Birgin Airlines is not the only one trying to look for alternative fuel sources. Earlier this year, an Airbus A380 used another alternative fuel-a man-made mix of gas-to-liquid, in one of its four engines. The flight was tested by Rolls Royce (manufacturer of jet engines), in partnership with Shell (an oil company). Rolls Royce is also working with Air New Zealand on a similar project. While a complete switch to alternative fuel may take years, it is very encouraging to see airlines, oil companies and airplane manufacturers all coming together to try to make it happen! .One of the hurdles to be overcome for a full biofuel switch is to  _  .
A. alter the engine for airplanes
B. make biofuel burn consistently
C. open more land to grow more crops
D. develop sewage treatment plants
Answer: