首先分析句子成分
his english has much improved為主句,時(shí)態(tài)是現(xiàn)在完成時(shí),故由此尋找引導(dǎo)時(shí)間狀語(yǔ)從句的選項(xiàng),
since 符合時(shí)態(tài)要求
故為D
而其余三項(xiàng)不可引導(dǎo)完成時(shí)態(tài)的狀語(yǔ)從句
考點(diǎn)為現(xiàn)在完成時(shí)其他三項(xiàng)時(shí)態(tài)應(yīng)是什么樣的？你好before，after，when引導(dǎo)的時(shí)態(tài)最常見(jiàn)的為一般過(guò)去式，Annie was born a few weeks before Christmas.安妮在圣誕節(jié)前幾個(gè)禮拜出生。After breakfast Amy took a taxi to the station.早飯以后，埃米乘出租車去了車站。when的時(shí)態(tài)太廣泛其實(shí)，該階段考查范圍比較窄，都是有重點(diǎn)的做好老師的講義就可以了