Use question words to ask questions and Q & A
Use question words: when, where, who, what, how
He bought three books yesterday. （bought: [bɔːt]）
谁买？
1. Who bought three books yesterday?
buy what?
2. What did he buy (prototype) yesterday? [ For not a subject, ask questions to use the auxiliary verb + prototype ]
What time to buy?
2. When did he buy three books?
[ Not subject to use auxiliary / be a verb question prototype + ]
Use words to ask questions and answer questions
how long，how far，how often，why + 助动词
1. They have been in China for three years.
How long have they been in China? [多久？完成时]
2. It is about 4 kilometers from Beijing to Xian.
How far is it from Beijing to Xian?
3. They come to visit me once a week.
How often do they come to visit me? [多久，频度]
4. She came late, beacuse she missed the bus.
Why did she come late?
[ Interrogative whether it contains auxiliary, modal verb, if any, appears to be a verb infinitive, the other is what which who directly as the subject, the latter may be tense verb according to. ]
The note finishing in Cui Rongrong teacher video to explain: https: //www.bilibili.com/video/av2639206