问题补充:
--- What useful book !
---Yes, it is. But I found difficult for me to read.
A. an, it was
B. a, it’s
C. an, it’s
D. a, it
答案:
A. an, it was
B. a, it’s
C. an, it’s
(答案→)D. a, it
解析:英语中不定冠词的用法是根据后续单词的词首音素,如果词首音素时元音,则用an,否则用a。上文useful词首音素为辅音,故不定冠词用a。下文it做形式宾语指代后面内容,故选D。