气孔主要分布于叶上表皮的植物一般适于生存于下列哪一生态环境中（）
A.旱生
B.水生或湿生
C.阴生
D.阳生
参考答案：C
An increasing number of students, year by year, across China ____ hard to realize their dream of studying abroad.
A．is trying
B．are trying
C．will try
D．have tried
《劳动法》第72条规定，用人单位和劳动者（）依法参加社会保险，缴纳社会保险费。
A.必须
B.应当
C.可以
D.能够
