已知的傅里叶级数展开式中,系数a3的值是()。
A.A
B.B
C.C
D.D
参考答案:C
对于控制晶粒度的方法,下列措施中属于控制过冷度的有()。
Ⅰ.降低浇铸温度;
Ⅱ.减小铸型温度升高的速度;
Ⅲ.加入人工晶核;
Ⅳ.增强金属液的运动;
Ⅴ.打碎正在生长的树枝晶。
A.Ⅰ+Ⅱ+Ⅳ
B.Ⅰ+Ⅱ+Ⅴ
C.Ⅱ+Ⅲ+Ⅴ
D.Ⅰ+Ⅱ
. ------- What do you think of Harry, our new roommate?
-------- I am not sure, but he is always asking ______ questions.
a great many of B. a great many C. a great number D. a large amount of