A.（19.75-17.29）÷0.81+0.4×0.5
B.[（19.75-17.29）÷0.81+0.4]×0.5
C.[19.75-17.29÷0.81+0.4]×0.5
D.19.75-17.29÷0.81+0.4×0.5

A.4.9+10.2÷5.1
B.4.9+5.1÷10.2
C.5.1÷（4.9+10.2）
D.（4.9+10.2）÷5.1

A.（7-5.2）×3+2.2÷4
B.7-5.2×3+2.2÷4
C.（7-5.2×3+2.2）÷4
D.[（7-5.2）×3+2.2]×4

A.加法结合率
B.乘法交换律
C.乘法分配律

A.8
B.4
C.16
D.32

A.230
B.231
C.232

A.8.2×3.5+6.21×3.5+6.21×3.5
B.（8.2+6.21×2）×3.5
C.6.21×（2+1+1）×3.5
D.6.21×[（2+1+1×3.5）]

A.1
B.0
C.10

A.2
B.0
C.1
D.3

A.a÷b
B.a×b
C.a－b
D.a＋b

A.8×7
B.9×7
C.9×6
D.8×6