Ответ:
13
2 , who was the school‘s headmistress fir ten years, ( NI can’t be omitted)
3 which /that ( I can be omitted)
4 who ( NI can’t be omitted)
5 , who was in my class at school, (NI can’t be omitted)
6 which /that ( I can be omitted)
7 which /that ( I can be omitted)
8 which/that ( I can’t be omitted)
9 whose ( I can’t be omitted)
10 , which I like very much, ( NI can’t be omitted)
11 who/that ( I can’t be omitted)
12 , who/whom I don’t know very well , ( NI can’t be omitted)
13 who/that ( I can be omitted)
15
A
2 who/that -can’t be omitted
3 where -can’t be omitted
B
1 whose- can’t be omitted
2 why/that- can be omitted
3 who/that -can’t be omitted
4 when/that -can be omitted
5 when/that -can be omitted
C
1 who/that -can’t be omitted
2 which/that -can be omitted
3 where -can’t be omitted
4 where - can’t be omitted
D
1 when/that -can be omitted
2 which /that -can be omitted
3 whom/who /that -can be omitted
4 which -can’t be omitted
5 why/that -can be omitted
6 why /that -can be omitted
7 who/that -can’t be omitted
E
1 who -can’t be omitted
2 whose -can’t be omitted
3 which/that -can’t be omitted
4 where can’t be omitted