更换调速级喷嘴组,对新喷嘴组应做哪些核查工作?
参考答案:
应核查结构尺寸,与拆下的旧喷嘴进行比较,特别要注意核对影响通流部分间隙的尺寸和喷嘴组的喷嘴数目。
下列说法中错误的个数是( )
①一个命题的逆命题为真,它的否命题也一定为真;
②命题“∀x∈R,x2-x≤0”的否定是“∃x∈R,x2-x≥0”;
③“矩形的两条对角线相等”的逆命题是真命题;
④“x≠3”是“|x|≠3”成立的充分条件.
A.1
B.2
C.3
D.4
By serving others, a person focuses on someone other than himself or herself, __________ can be very eye-opening and rewarding.
A.who
B.which
C.what
D.that