（1）原式=2×2+2×2
=2+22；
（2）原式=3×3+3×13
=3+1
=4．
Don't mention that at the beginning of the story, or it may _____ the shocking ending.[ ]
A. give away
B. give out
C. give up
D. give off
为了防止基底土（特别是软土）受到浸水或其他原因的扰动，使用单斗挖土机时预留土层厚度为（）cm，暂时不挖。
A.20～30
B.15～20
C.10～15
D.5～10
