The wall of pollen grain is divided into two layers. A: primary wall and secondary wall B: pectin layer and primary wall C: outer wall and inner wall D: pectin layer and secondary wall

Be careful! ________. A: The wall is falling B: The wall is to fall C: he wall will fall D: The wall is going to fall

The Romans built two walls to keep the picts out of the area they had conquered. The two walls were called ______ and ______. A: the picts’ Wall, Celts’ Wall B: the Hadrian’s Wall, the Antonine Wall C: Britain’s Wall, Scotland’s Wall D: Roman Wall, Julius’ Wall

What did the “fourth wall” in drama refers to? A: the wall on the left side of stage B: the wall on the right side of the stage C: a virtual wall D: the wall at the front part of stage near to the audience

If all parties announce that their positions cannot be changed, then the negotiation process will turn into _______________.( ). A: a wall of will B: wall of wills C: a wall wills D: a wall of wills

The light on the wall turns off. The light on the wall ______.

For walls, a（）is a slab wider than the wall and extending the length of the wall

John has been to the Great Wall.____________. A: So he did B: So did he C: So he has D: So has he

Between the outside wall of glass and the two inside walls of glass, there is ______. A: an empty space B: another huge wall C: a triple-glazed wall

One of the differences between the outer wall and the inner wall of pollen is that the outer wall contains the following substances: A: protein B: cellulose C: sporopollenin D: protein and sporopollenin