Choose the correct words

1. The children promised to make a serious [effort|try] to get along.
2. The employees tried to adopt a more [capable|effective] way of sharing files.
3. They have studied the contract [vastly|extensively] and have agreed to all the terms.
4. He makes a(n) [substantial|important] amount of money from his part-time job.
5. Plastic food wrapping is one of the health [hazards|dangers] that we face daily.
6. It's too [uncertain|risky] to go hiking alone in the mountains.
7. Smokers are more [vulnerable|tender] to heart attacks than non-smokers.