读某地地层剖面示意图，回答第下面问题。
图中各岩层的形成，按由先到后顺序排列正确的是（）
A.③---②---①---④
B.①---③---②---④
C.②---①---③---④
D.①---②---③---④
参考答案：D
解析：
①岩层具有层理构造，说明属于沉积岩，据图例可知②③属于侵入型岩浆岩，并且③切穿②，说明②先形成③后切入其中，而②③又都切穿沉积岩层①，所以②③应在①形成之后形成。后来该地地壳下沉，又接受沉积，形成④上覆岩层。故先后顺序排列正确的是D选项。
| Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root. Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently. So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species. |
Which of the following can be inferred about the effect of direct sunlight on lichens
A．It damages the algae.
B．It helps the fungi absorb water.
C．It is required for the algae to carry on photosynthesis.
D．It destroys the fungi.