Jack and Mike were found cheating in the exam, and _____by their teacher at the moment.[ ]

I have reached a point in my life _____ I am supposed to make decisions of my own.

－ Whose isthis blue bike －It ________be Mary’s. Her bike is black and white.

There’re_____in the library,and you are _____to read any book you want to read.

You promised your friend a letter; youought to ______ days ago.