问题补充:
His arms were sunburnt because he in the sun all day.
A. had sat
B. sat
C. is sitting
D. had been sitting
答案:
A. had sat
B. sat
C. is sitting
(答案→)D. had been sitting
解析:考查时态。本句中的all day一整天,该短语与完成进行时连用,根据前半句的were说明只有过去完成进行时的形式,句意:他的胳膊赛坏了,因为一整天他都坐在阳光下。故D正确。