(C) they used trans-Saharan trade route to acquire expensive ivory.
D because to help preserve environment everyone has to work together
D) It can only be used in areas with specific kinds of rivers.
Answer:
The answer is a. they are much like empty rooms.
Explanation:
Cells are pretty much the opposite of empty rooms. There are many organelles and processes happening in them, so there's no space for empty rooms. Even when there are spaces, which anyway would be full of liquid, these spaces have a purpose.
