日光灯用久了以后，灯管两端会出现黑斑，这些黑斑是钨丝中的钨[ ]
A. 汽化而成
B. 升华而成
C. 先升华后凝华而成
D. 先汽化后凝华而成
答案：C
The Diaoyu islands have been part of China’s territory since ancient times, ______ as important fishing grounds of Taiwan.
A．served
B．to serve
C．serving
D．having served
异位妊娠最常见的部位在何处（）
A.卵巢
B.腹腔内
C.输卵管
D.阔韧带
E.宫颈
