One of the most important questions they had to consider was _____ of public health. 

My opinion about the modern education is not similar to _________of the other teachers’.

Nowadays everything strange is ________ strange. That is to say, any unexpected thing is possible to happen.

 Don’t waste your time in your holiday. Try to find _______ useful to do. 

Mr. Lee made ______ a rule that we must come to school on time.