1. We could had done more if we had had more time. --> have
2. He said that if he has more time , he would come to see us. --> had
3. While I did my homework , I had a good idea. --> was doing
4. Don't make so much fusses over the children. --> fuss
5. John's friends had celebrated a farewell party for him last Sunday. --> celebrated
1, could had ⇒ could have
2, has ⇒ had
3, did ⇒ was doing
4, fusses ⇒ fuss
5, had celebrated ⇒ celebrated