Usage of preposition +which

1, the "preposition ++which" indicating place, time and reason is equivalent to where, when and why respectively.

The earth where we live is a planet.

I will never forget the day when I joined the League.

2. It is often used instead of which after way, or it can be omitted.

That's how the old lady takes care of us.

3. "of+which" acts as an adjective, equivalent to "who", and its word order is usually "n.+of+which".

They live in a house whose door faces south.

Principles of choosing prepositions:

1, according to the habitual collocation of predicate verbs in attributive clauses

Is this the book? On which one? I spent eight dollars.

Is this the book? For what? I paid 8 dollars.

2. According to the collocation habits of antecedents

I remember those days? What about the period? I live there.

I remember that day? On which one? I graduated from college.

3. Decide according to the meaning expressed in the whole sentence

Colorless gas? No one? What we can't live is called oxygen.

In order to emphasize a noun in English, relative pronouns can also be added before infinitives.

This is money, which one is used? Go and buy a piano.

She is the right person to rely on.