3. a) Match sentences 1-4 with their meanings a-d.
1. Students must be
very careful climbing
the mountains.
2. Boys and girls mustn't study
in one class.
3. A lot of children have to
take boats to go to school.
4. In some schools, students
don't have to study these
subjects.
a) It's not necessary/
obligatory.
b) Do this. It's very
important.
c) It's not allowed. Don't
do it.
d) It is necessary to do.
You don't have
a choice.