在冶炼和焊接的过程中（）是重要的脱氧剂。
A.C
B.Zn
C.Ca
D.Mn
E.Ti
参考答案：D
______ is the first day of the week, but we don't go to school on it. [ ]
A. Sunday
B. Monday
C. Saturday
D. Tuesday
对于实数λ≠0，非空向量零向量，下列各式正确的是()．
A.A
B.B
C.C
D.D
零向量
，下列各式正确的是()．