A:when does his son come back
B:when his son comes back
C:when his son come home
D:when his son came home
探究题:取一块馒头放在口里咀嚼,细细品味时,会尝出一些甜味来,并且会越嚼越甜.这与馒头中淀粉在口腔里的变化有关.某实验小组将少许馒头切碎,平均分成A、B两份,作如图处理.请根据实验回答问题:
如图,三视图描述的实物形状是( )
下列行为都是人们为了解决某些环境问题采取的措施,哪一项措施最容易导致相反的效果( )