678+419+322
=678+322+419
=1000+419
=1419
①SiO2﹣→Na2SiO3;②CuSO4﹣→CuCl2;③SiO2﹣→H2SiO3 ;④CuO﹣→Cu(OH)2;⑤Na2O2﹣→NaOH.
—Thanks a lot.
⑴play football ____ A.那些男孩们
⑵on the playground ____ B. 观看比赛
⑶watch the games ____ C.踢足球
⑷play volleyball ____ D. 在操场上
⑸those boys ____ E. 打排球