Question

1. This is the house where he lives.
2. This is the house in which he lives.
3. This is the house that/which he lives in.
4. This is the house that he lives.
5. This is the house he lives.
6. This is the house he lives in.
==============
Among the 6 sentences, #4 and #5 are incorrect? Am I right? Are the others grammatical?

7. I don't know the way how he solve the problem.
8. I don't know how he solve the problem.

==================
#7 is wrong. #8 is right. We have to omit either 'the way' or 'how.' Then what is the part of speech of 'how' in Sentence 8? Is 'how' an interrogative adverb or a relative adverb?

Answer 1

You are right that 4 and 5 are incorrect. All the others are fine.

7 is incorrect, yes.

8 will be correct if you write it like this: I don't know how he solved the problem. (second verb is past tense)

"how" in this sentence is serving as an interrogative word to introduce an indirect question.