10以内（包含10）所有合数的和与所有质数的和相差______．

— Is your present pension sufficient to cover your cost of living?

— Enough and to spare. _____[ ]

A. I can't complain.

B. Serve me right!

C. I've had enough of it.

D. I can't be too particular.

GMP

某建筑物首层地面标高为±0.000m，其绝对高程为46.000m；室外散水标高为-0.550m，则其绝对高程为（）m。

A.-0.550

B.45.450

C.46.550

D.46.000

当超声波的波长与金属晶粒相比，数值相近，或小于晶粒时，（）显著、穿透能力减弱，同时由于晶粒反射，出现（）回波，不易检出缺陷。

什么是安全系统工程？