—What do you often do _______ classes to relax yourselves?
— We often chat together, do eye exercises or do some running around the school.
受精卵的形成场所和胚胎发育的场所分别是( )
等比数列an的首项为1,公比为q,前n项的和为S,由原数列各项的倒数组成一个新数列1an,由1an的前n项的和是( )
在家庭电路中,火线和零线之间的电压是 ____V;图中哪些图所示情况会发生触电事故: ____.