肺由大量的肺泡构成，其重要意义是 [ ]
A．使肺内贮存的气体量增多
B．增大了肺进行气体交换的面积
C．使肺泡内氧的含量增加
D．使气体流通加快
答案：B
With a lot of difficulties _______, they went to the seashore and had a good rest.
A．settled
B．settling
C．to settle
D．being settled
—Is the blue ruler _______?
—No. _______ ruler is red.
A．your; My
B．yours; My
C．yours; Mine
D．your; Mine
