He hurried to the station only _______ that the train had left.
A:to find
B:finding
C:found
D:to have found
面对环境污染严重、生态系统退化的严峻形势,党的十八大报告指出,必须树立尊重自然、顺应自然、保护自然的生态文明理念.请回答下列问题:
脂肪和核酸所共有的化学元素是( )
下列大洲之中,无极昼、无极夜现象,但有阳光直射现象的是( )