① put litter into the dustbin
② stay up reviewing lessons all the time
③ go to school without breakfast
④ wash hands before meals
⑤ open the window and take a fresh breath as often as possible
A:①④⑤
B:②③④
C:①②⑤
写一写综合实践活动总结。450字左右。
①之:父命之____ 往送之门____ 立天下之正位____
②行:行天下之大道____ 行拂乱其所为____
③发:舜发于畎亩之中____ 发于声____
④为:行拂乱其所为____ 以顺为正者____
已知各项为正数的等差数列{an}的前20项和为100,那么a7·a14的最大值为( )