They got two free tickets to Canada; otherwise, they'd never have been able to ______ to go there.
A:admit
B:avoid
C:appreciate
D:afford
____时
____:____
正在生长发育的青少年需要大量的蛋白质,为补充蛋白质应该多吃哪种食物:( )
已知函数fx=lnex-e-x2,则fx是( )