What has sometimes caused plants to die out in the past? A.Variations in climate. B.The introduction of new types of plants. C.The absence of wooded land. D.Interference from the foresters.
Đáp án đúng: A Giải chi tiết:Đáp án là A. Dựa vào ý: Plants have minimum requirements of temperature and moisture and, in ages past, virtually every part of Earth’s surface has, at some time, been either too dry or too cool for plants to survive.