Question

1、 they are at a loss to know ---- they should look for the

Answer 1

1）they are at a loss to know --where-- they should look for the lost child

词组at a loss茫然不知所措

他们不知道该到哪儿去找那个走丢的孩子

表示地点的宾语从句

到哪儿去找,自然要用where了

2）a survey is carried out on the death rate of new-born babies in that region,--the result of which---were surprising

那个地区的新生儿死亡的调查结果令人惊讶

是非限制性定语从句

which指代前面的the result