Sorry to say, both answers above are wrong! The correct answer is A: "It's high time the girl WERE sent to school." D, "The girl is to be sent to school," means something like: there are plans to send the girl to school. B, In a Past Subjunctive construction, one should use 'were', instead of 'was'. Although you will see "It's high time the girl was sent to school" a lot in daily life. Answer 'C' can be correct too: "Isn't it time the girl BE sent to school?"

Nevermind, see above.

the answer is definitely 'was' Not sure why - perhaps this construction needs it because you are describing something that should already have happened, ie, she should have been sent to school.

It's high time that the girl is to be sent to school. 不定式的一种用法，表示，应该，要。等于The girl should/must be sent to school.