Answer:
1. --> whoever wants to help
2. --> who is behind the counter
3. --> when I press the button
Explanation:
Dependent or subordinate clauses are the ones that do not express a complete thought by themselves. They need the information in the main clause to make sense. Imagine your friend walks up to you, says hi and then, "After I got home last night..." You will certainly ask, "After you got home what?" That is because your friend gave you a subordinate clause with no main clause to fill in the missing information. Dependent clauses start with subordinate conjunctions (when, after, that, whoever, whenever, who etc.) and can function as a noun, an adjective, or an adverb.
In number 1, we have a nominative or noun clause functioning as the subject: Whoever wants to help is invited to come with us.
In number 2, we have an adjectival clause modifying the noun "person": Talk to the person who is behind the counter.
In number 3, we have an adverbial clause showing when something happens: When I press the button, the computer starts up.
