从担任“村官”到自主创业，从下基层到走进西部，越来越多的高校毕业生找到了更为宽广的就业之路。这启示我们

①要树立正确的就业观念     ②选择职业要兼顾社会需要与个人专长

③要坚持多元化的就业选择   ④转变观念是实现就业的关键

A．①②③

B．①③④

C．①②④

D．②③④

Experts are trying to work out a plan to deal with the problems caused by global warming _________ it is too late.

A．if

B．before

C．when

D．until