"The world has never been a better place to live in," says science writer Matt Ridley, "and it will keep on getting better." Ridley's critics have accused him of his views on climate change and the free market. Yet Ridley, 54, sticks to his guns. "It is not mad to believe in a happy future for people and the planet," he says. Ridley, who's been a foreign correspondent, a zoologist, an economist, and a financier, brings a broad view to his sunny outlook. "People say I'm crazy to claim the world will go on getting better, yet I can't stop myself," he says. Read on to see how Ridley makes his case. Compared with 50 years ago, when I was just four years old, the average human now earns nearly three times as much money, eats one third more calories, and can expect to live one third longer. In fact, it's hard to find any region of the world that's worse off now than it was then, even though the global population has more than doubled over that period. City citizens take up less space, use less energy, and have less impact on natural ecosystems than country livers. The world's cities now contain over half its people, but they occupy less than 3 percent of its land area. Urban  growth may worry environmentalists, but living in the country is not the best way to care for the earth. The best thing we can do for the planet is build more skyscrapers. The rich get richer, but the poor do even better. Between 1980 and 2000, the poor doubled their consumption. Nigerians are twice as rich and live nine more years. The percentage of the world's people living in   poverty has dropped by over half. The United Nations estimates that poverty was reduced more in the past 50 years than in the previous 500. Ridley's attitude toweards the human future is   _  .
worried proud concerned optimistic
Question: "The world has never been a better place to live in," says science writer Matt Ridley, "and it will keep on getting better." Ridley's critics have accused him of his views on climate change and the free market. Yet Ridley, 54, sticks to his guns. "It is not mad to believe in a happy future for people and the planet," he says. Ridley, who's been a foreign correspondent, a zoologist, an economist, and a financier, brings a broad view to his sunny outlook. "People say I'm crazy to claim the world will go on getting better, yet I can't stop myself," he says. Read on to see how Ridley makes his case. Compared with 50 years ago, when I was just four years old, the average human now earns nearly three times as much money, eats one third more calories, and can expect to live one third longer. In fact, it's hard to find any region of the world that's worse off now than it was then, even though the global population has more than doubled over that period. City citizens take up less space, use less energy, and have less impact on natural ecosystems than country livers. The world's cities now contain over half its people, but they occupy less than 3 percent of its land area. Urban  growth may worry environmentalists, but living in the country is not the best way to care for the earth. The best thing we can do for the planet is build more skyscrapers. The rich get richer, but the poor do even better. Between 1980 and 2000, the poor doubled their consumption. Nigerians are twice as rich and live nine more years. The percentage of the world's people living in   poverty has dropped by over half. The United Nations estimates that poverty was reduced more in the past 50 years than in the previous 500. Ridley's attitude toweards the human future is   _  .
A. worried
B. proud
C. concerned
D. optimistic
Answer: