選C
解析如下：
此句陳述部分是表轉(zhuǎn)折關(guān)系的并列句,附加疑問(wèn)句則需和就近的分句的主語(yǔ)和謂語(yǔ)一致.由此可以判斷應(yīng)該對(duì)后半句進(jìn)行反問(wèn).
Tom has been writing letters all afternoon,but he should have finished them by now,______?
湯姆整個(gè)下午都在寫信,那他現(xiàn)在應(yīng)該寫完了,_是嗎___?
b.has he 不符合反意疑問(wèn)句前肯后否的原則
d.didn't you 時(shí)態(tài)和人稱都不符合答案
a.hasn't he?如果此選項(xiàng)可選那么應(yīng)改為如下形式
but he should finish them by now,______?
即should do 表示對(duì)現(xiàn)在的推測(cè),而反意疑問(wèn)句要對(duì)即存事實(shí)進(jìn)行反問(wèn),所以為
hasn't he?此用法可參照Must 在反意疑問(wèn)句中的用法.
而原文 he should have finished ...其中的"should"就是一個(gè)單純的情態(tài)動(dòng)詞
修飾現(xiàn)在完成時(shí).表推測(cè)和表虛擬都與"by now"時(shí)態(tài)不符.
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