Between the two parts of the concert is an interval, _______ the audience can buy ice-cream.
Some scientists think there are _______ 2,000 million flashes of lightning per year.
Whenever we are in ______ trouble, we should never lose______ heart.
We all know that, __________, the situation will get worse.
—Can I join the club, Dad? —You can when you _____ a bit older.
If you are in any doubt as to _____ you should be doing these exercises, consult your doctor.