I haven't seen that man here before =>It's... The furniture was so expensive that I didn't buy it => The furniture was too.... Tom learned to drive when he was nineteen (since) => She had never been so unhappy before (than) => It was so late that nothing could be done(too) =>

1. It's the first time I have seen that man here. ( it's the first time + HTHT)

2. The furniture was too expensive for me to buy. ( too adj for sb to V)

3. Tom has learned to drive since he was nineteen. (HTHT since QKĐ)

4. She was unhappier than she had been before.

5. It was too late for anything to be done