The missing boys were last seen ________ near the river.
A
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。
Themissingboyswerelastseen________neartheriver.
IntheU.K.,theQueen'sSilverJubileeisin_______.
Thevisitingministerexpressedhissatisfactionwiththetalks,________thathehadenjoyedhisstayhere.
______alittleearlier,Iwouldhavecaughtthetrain.
It_______fortwohoursnow