_____explanation is necessary.
.The petrol tank is empty.I _________it up before we left home.
Driving a car is not as difficult as you imagine,if you_________ the rules.
When Mr.Jones gets old,he will _________ over his business to his son.
Mrs.Brown is supposed _________ for Italy last week.
The water of a hot spring carries many minerals,usually _________ us an unusual taste and smell.