Only after his friend came _______.
Not only ____________ vital for reducing fever and helping stop pain, but there are also other things that aspirin can help with.
It was not until 1938 _________ the first colour TV programme was broadcast.
You can borrow my car ________ you promise not to drive too fast.
We were told not to touch the equipment in the laboratory unless ________.
If you cannot have a good command of grammar as well as precise usage of each word you’ve learnt, it is ________ for you to use English flexibly.