What’s this?It’s .A. an ID card B. a orangeC. rulerD. an UFO

问题补充：

--- What’s this?

--- It’s .

A. an ID card

B. a orange

C. ruler

D. an UFO

答案：

(答案→)A. an ID card

B. a orange

C. ruler

D. an UFO

解析：A. an ID card I的发音是[ai]元音，故用an; B. a orange [??]元音开头，故用an,错误。

C. ruler 可数单数名词不能单独用，要在前面加a; D. an UFO [ju: ef ??]第一个发音是辅音，所以用 a,选项错误。故选A