The missing boys were last seen ________ near the river.
A、playingA
所填的词为主语补足语，因其后有明确的地点，补足语表示动作当时正在进行中，所以只能使用playing。
Asforfamilyeducation,parentsareencouragedtorelyon________ratherthanpunishment.
Bythemiddleofthe21stcentury,thevastmajorityoftheworld’spopulationwillbelivingincities_______inthecountry.
Thepolicemancameuptothelonelyhousewiththedoor_______,_______thereforawhileandthenenteredit.
______ is recognized as the national flag-carrier.
The first task of a brochure is to _______.
