21
[答案]:C
[解析]:参见教材P271
22
[答案]:B
[解析]:参见教材P242
23
[答案]:B
[解析]:参见教材P242
24
[答案]:D
[解析]:参见教材P242
25
[答案]:D
[解析]:参见教材P242
26
[答案]:C
[解析]:参见教材P242
27
[答案]:A
[解析]:参见教材P242
28
[答案]:C
[解析]:参见教材P244
29
[答案]:C
[解析]:参见教材P245
30
[答案]:B
[解析]:参见教材P245
31
[答案]:D
[解析]:参见教材P246
32
[答案]:C
[解析]:参见教材P246
33
[答案]:D
[解析]:参见教材P246
34
[答案]:B
[解析]:参见教材P246
35
[答案]:A
[解析]:参见教材P246
36
[答案]:B
[解析]:参见教材P246
37
[答案]:B
[解析]:参见教材P253
38
[答案]:A
[解析]:参见教材P247
39
[答案]:A
[解析]:参见教材P253
40
[答案]:A
[解析]:参见教材P248
41
[答案]:A
[解析]:参见教材P248
42
[答案]:A
[解析]:参见教材P253
43
[答案]:A
[解析]:参见教材P253
44
[答案]:C
[解析]:参见教材P254
45
[答案]:A
[解析]:参见教材P255
46
[答案]:B
[解析]:参见教材P255
47
[答案]:D
[解析]:参见教材P256
48
[答案]:D
[解析]:参见教材P256
49
[答案]:C
[解析]:参见教材P260