Rewrite the following sentences in such a way that they mean the same as the original sentences

II. Rewrite the following sentences in such a way that they mean the same as the original sentences.
  1. Work hard and you will pass the exam.
$\to$If you ............................................
  2. He took a lot of photographs even though the sky was dark.
$\to$Despite ..............................................
  3. It's three years since I last saw him.
$\to$I haven't .........................................
  4. Alexander Graham Bell invented the telephone in 1847.
$\to$The telephone .............................................