3. Mr. Lam should wear gloves to protect his hand.

=) Mr. Lam had better.....wear gloves to protect his hand .........
4, He always washes his hands before meals. She always washes her hands before meals.

=) He always washes his hands before meals. So does she

5, I didn't have a toothache. They didn't have a toothache

=) I didn't buy new books and neither did they.