Can we always answer every "How" question with "by + gerund"?
For example, "Q: How did you pass the exam? Ans: By working hard."
I think not every "How" question can be answer with "by + gerund".
For example, "Q : How did he become rich? Ans: Because a book he wrote became a best-seller in 16 countries."
I think we cannot answer the question in my second example with "by + gerund".
Am I right? If not, someone correct me please.
"Q: How did you know my address? Ans: Your classmate gave me."
I wonder if "by+gerund" can be used for this one.
I was wrong in saying "every 'how' question. I should have said "'how' questions with action verbs, asking about deliberate actions.
What I mean is "by + gerund should be used in answer only when the action is a deliberate one.
A: How did you know my address?
B: I overheard someone mention it on the bus." ("By overhearing someone mentioning it on the bus"). This is not a deliberate action. (At least B might claim it was not deliberate to listen to someone else's conversation.)
"How" can mean various things. If the meaning is "By what mechanism ...?", you could normally use a "By ....ing ...." answer.