Vitamin D helps our bodies make a special chemical,and this special chemical, ______ affects our brains,making us feel happy.
I just wonder _____ that makes him so excited.
He got run over by _____ taxi and now he is still in ____ danger in hospital.
I can’t _____ his failure.It is unbelievable.
—Who left the door open?— Oh, sorry. I _____ the door.
The traffic problems we are looking forward to ______ solved should have attracted the government’s attention.