Read the following short paragraphs and decide the way this paragraph uses to develop its controlling idea. Last year many of the village people in this area had to leave home to find jobs in neighboring towns and cities after the area was hit by a severe drought which led to a considerable drop in the production of crops.

A.One single cause leads to multiple effects.

B.One single effect is caused by multiple reasons.

C.One single cause leads to one single effect.

D.A causal chain.

正确答案：A causal chain.