山体越高，垂直带谱越（）。
A．简单
B．复杂
C．不变
参考答案：B
She is very heavy, ______ she never stops eating.
A．so
B．but
C．if
D．when
The scientist decided to devote his life to ____ pollution from ____ again.
A．preventing; happening
B．prevent; happen
C．preventing; happens
D．preventing; will happen
