_________ socks 20 dollars? [ ]
A. Is the
B. Are they
C. Are the
D. Is that
答案:C
晶体中渗入杂质或由较为纯净的晶体形成了非整比化合物都属于化学缺陷。
电力系统单相(A相)接地时,故障点处的三个边界条件分别为()。