5. It was cold .however ,tom still went swimming(although)

--> Although it was cold, Tom still went swimming.

6. John is very sad .He fails the final exam(because)

--> John is very sad because he fails the final exam.

7. He never left the house .He had been born there(where)

--> He never left the house where he had beeb born.

8. I met the man .He works in a bank (who)

--> I met the man, who works in a bank.

9. Here are the letters .they arrived this morning(which)

--> Here are the letters which they arrived this morning.

10. My grandfather is very old .he is still young at heart (although)

--> Although my grandfather is very old, he is still young at heart.