光、热、水、气和养分等是对生物生长发育起______作用的生态因子。
参考答案：直接
When we meet some new words, we'd better ______ in a dictionary.[ ]
A. look out them
B. look them out
C. look them up
D. look up them
我国的旅游保险有强制性的旅游保险，也有自愿购买的旅游保险。
