Over a period of time, many habitats (栖息地)change with respect to the types of plants and a

Over a period of time, many habitats (栖息地)change with respect to the types of plants and animals that live there. This change is known as succession.
Succession occurs because plants and animals cause a change in the environment in which they live. The first weeds and grasses that appear on a bare field, for example, change the environment by shielding the soil from direct sunlight. As these plants spread, the ground bees cooler and more moist than it was originally. Thus, the environment at the ground surface has been changed. The new surface conditions favor the sprouting（产生）of shrubs. As shrubs grow, they kill the grasses by preventing light from reaching them and also enhance (增加)the soil. Pine seedlings (苗)soon take hold and as they grow, they in turn shade out the shrubs. They are not able to shade out oak and hickory (山核桃)seedlings, however, that have found the forest floor suitable.  These seedlings grew into large trees that eventually shade out the pines.
【小题1】The best title of this passage is     .A．The Importance of Weeds and GrassesB．The Success of Oak and HickoryC．How Environmental Habitats ChangeD．Animal and Plant Habitats【小题2】It can be inferred (推理) from the passage that     .A．oak and hickory trees grow taller than pinesB．weeds and grasses prefer cold climateC．pines and grasses can exist togetherD．birds encourage the growth of shrubs【小题3】 Which of the following is a stage of succession as described in the passage?A．A forest cut down to build an airport.B．A flood washing away a crop of wheatC．Wild flowers growing in an unused parking lotD．Animals being tamed (驯服)by childrenC