定态的圆筒壁传热，热通量为常数。
A. 对
B. 错
What can help to change the situation of agriculture market to work for the poor?
A. Digital technology
Banks
C. Extension workers
D. Local cooperative
Which of the following statements about Africa is not true?
A. Hundreds of millions of African people live on farming.
B. Half of the labor in Africa produces food.
C. Africa imports $40 billion worth of food this year.
D. African smallholders failed to grow as much food as they could.
Why aren’t African smallholders take advantage of the %40 billion food market?
A. Farmers and markets can’t communicate effectively.
B. There are no rails and roads to take crops to the market.
C. They grow mostly what they can eat or trade locally.
D. They lack of farm-management practices.
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