1. Giving care and comfort to the poor and sick is our happiness.
2. What is the best way to raise money to support charities?
3. Having passed the entrance exam, he was allowed to go away for the holiday.
4. They warned the children that swimming in this lake is dangerous.

1. The teacher suggested helping the people in the remote areas in summer.
2. There has been a considerable decrease in the number of injuries from automobile accidents this year.
3. Peter advised me not to cheat in the exams.
4. Having finished his homework, Tom went to bed.

Giving care and comfort to the poor and sick is our happiness. (The verb should agree with the subject in number.)

1. What is the best way of raising money to support charities? (The verb "raise" is more appropriate for gathering funds.)
2. Having passed the entrance exam, he was allowed to go away for holiday. (The past participle "having passed" is used correctly to show a completed action before the main clause.)
3. They warned the children about swimming in this lake. It's dangerous. (The sentence is correct.)

1. The teacher suggested that I/we help the people in the remote areas in summer.

1. There has been a considerable decrease in the number of the injured from automobile accidents this year.
2. Peter advised me not to cheat in the exams.
3. Having finished his homework, Tom went to bed.