• human + who + verb
• human + whom + sentence (subject + verb)
• non-human + which + verb
• non-human + which +sentence (sunject+ verb)
• human / non-human+ whose + noun

IELTS Writing:

• Task 1: A letter (+150 words/ in less than 20 minutes)
• Task 2: An essay (+250 words/ in nearly 40 minutes)

letters:

• formal
• informal