In this section, you will hear one passage. At the end of the passage, you will hear four questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D).A、Scientists are still not sure about how tree roots work.
B、A tree trunk is made of tiny tubes.
C、Tree roots can take in air from the soil.
D、All trees take in water, air and nutrients through the roots.