地球早期的生命起源和生物进化大致经历了()阶段、()阶段、()阶段、()阶段(裸露动物群)和()阶段。
参考答案:化学演化,原核生物,真核生物,无壳后生生物,带壳后生生物
Please tell Tom not to leave the classroom unless he ______ that all the lights ______.
A.makes sure; are turned off
B.makes sure; will be turned off
C.is made sure; are turned off
D.will make sure; will be turned off
人口增长过快给社会带来哪些问题?