Explanation:

Correct Answer is (a).The given statement wants to imply that all the students were present but the Principal did not come and the given parts in bold have errors since turn down refers to rejecting something especially a proposal by somebody and also, if the subjects are preceded by every, the verb used with such subjects should be singular. Here were has been used with every boy and girl, this is not correct usage.
Hence, the correct sentence would be: Though every boy and girl was present, the Principal did not turn up.Turned off refers to left one road to join another whereas turned on refers to attacked suddenly with full power.Hence, option A is the correct choice among the given options.