The idea of being able to walk on water has long interested humans greatly. Sadly, biological facts prevent us ever accomplishing such a thing without artificial aid--we simply weigh too much, and all our mass pushes down through our relatively small feet, resulting in a lot of pressure that makes us sink. However, several types of animals can walk on water. One of the most interesting is the common basilisk. Basilicus, a lizard   native to Central and South America. It can run across water for a distance of several meters, avoiding getting wet by rapidly hitting the water's surface with its feet. The lizard will take as many as 20 steps per second to keep moving forward. For humans to do this, we'd need huge feet that we could bring up to our ears in order to create adequate "hitting. " But fortunately there is an alternative: cornflour. By adding enough of this common thickening agent to water (and it does take a lot), you can create a "non-Newtonian" liquid that doesn't behave like normal water. Now, if the surface of the water is hit hard enough, particles  in the water group together for a moment to make the surface hard. Move quickly enough and put enough force into each step, and you really can walk across the surface of an adequately thick liquid of cornflour. Fun though all this may sound, it's still rather messy and better read about in theory than carried out in practice, if you must do it, then keep the water wings handy in case you start to sink--and take a shower afterward! Walking on water hasn't become a reality mainly because humans   _  .
are not interested in it have biological limitations have not invented proper tools are afraid to make an attempt
Question: The idea of being able to walk on water has long interested humans greatly. Sadly, biological facts prevent us ever accomplishing such a thing without artificial aid--we simply weigh too much, and all our mass pushes down through our relatively small feet, resulting in a lot of pressure that makes us sink. However, several types of animals can walk on water. One of the most interesting is the common basilisk. Basilicus, a lizard   native to Central and South America. It can run across water for a distance of several meters, avoiding getting wet by rapidly hitting the water's surface with its feet. The lizard will take as many as 20 steps per second to keep moving forward. For humans to do this, we'd need huge feet that we could bring up to our ears in order to create adequate "hitting. " But fortunately there is an alternative: cornflour. By adding enough of this common thickening agent to water (and it does take a lot), you can create a "non-Newtonian" liquid that doesn't behave like normal water. Now, if the surface of the water is hit hard enough, particles  in the water group together for a moment to make the surface hard. Move quickly enough and put enough force into each step, and you really can walk across the surface of an adequately thick liquid of cornflour. Fun though all this may sound, it's still rather messy and better read about in theory than carried out in practice, if you must do it, then keep the water wings handy in case you start to sink--and take a shower afterward! Walking on water hasn't become a reality mainly because humans   _  .
A. are not interested in it
B. have biological limitations
C. have not invented proper tools
D. are afraid to make an attempt
Answer: