At the gate of the exhibition hall ,we were requested to ___ our tickets.
―Who are those people walking along the street with banners?―A group _______ itself the League for Global Environment Protection.
_____ human beings live in great numbers, the waters are very likely to become contaminated.
_____ I admit that the problems are difficult , I don’t agree that they cannot be solved.
It was found that although the girl could perceive things with her fingers, this ability ceased _____ her hands were wet.
______ you understand this rule, you’ll have no further difficulty.