Interrogative and exclamatory adjectives and pronouns

The interrogative and exclamatory adjectives CHE, QUALE, QUANTO can be used as pronouns when the sentence is interrogative or exclamatory. Examples:

A che pensi? (What are you thinking about?)
Dimmi che ti passa per la mente. (Tell me what’s going through your mind.)
Non so proprio che fare! (I just don’t know what to do!)
A quale dei due devo credere? (Which of the two should I believe?)
Quanto ci metterai per deciderti? (How long will you take to decide?)

The pronoun CHE can be replaced by CHE COSA or just COSA. Examples:

Che desideri?/ Che cosa desideri?/ Cosa desideri? (What would you like?)
Che è successo?/ Che cosa è successo?/ Cosa è successo? (What happened?)

As well as these forms, there is also the pronoun CHI which is used to refer to people or animals. Examples:

Chi bussa alla porta? (Who’s knocking on the door?)
Con chi vai in vacanza? (Who are you going on holiday with?)
Di chi è la colpa? (Whose fault is it?)
Da chi è andato Mario? (Who did Mario go to?)
A chi vuoi mandare gli auguri? (Who do you want to send greetings to?)
Su chi vuoi scommettere? (Who do you want to bet on?)