I often saw the boys in the river.

Could you please help me clean the living room– ,mum.

Who would you rather ________ the English Speech Contest? —- Li Ping, I think , is the best choice.

Some researchers believe that there is no doubt______a cure for AIDS will be found.

填入下面文段空白处的词语，最恰当的一组是比尔﹒布莱森在他的《万物简史》里介绍了超级火山的巨大破坏性。以美国为例，①境内有一座超级火山喷发，②其产生的巨大能量将摧毁数千公里范围内的所有东西，无数人会因此丧命，③会导致整个国家被深达6-20米的火山覆盖，随后④会出现其他许多可怕后果，⑤目前人类还无法预测美国超级火山在何时喷发，⑥了解了它的杀伤力有利于我们制订各种减损预案。 ①  ② ③ ④ ⑤ ⑥