It depends. We would need the context to tell you. It is she that goes out late at night and does not return until the morning. It is her book that is on the table.

http://www.thefreedictionary.com/taught Top left there are two buttons, an american flag, and a UK flag. Click either to hear the pronunciation

It means he got an illness, or he contracted an illness. Using developed also suggests a progression, in this case the he got a disease which was getting worse.

They mean the samething. However, pounding suggests a heavier beat. I can feel my heart beating now, but if I run for 20 minutes then my heart will be pounding!

You dont have to. The sentences are very good! I even had to look up truculent - and im a fairly well educated native speaker!

Imagine you have done jump and landed on your back. You are laying on your back. When you are in bed you might lay on your back, or lay on your side or even lay on your front. If you are laying on your back you will be looking up at the sky :-)

This depends on exactly where the speakers are in relation to the door. Your sentence is correct, but this would mean that the speakers are still at door and are going to leave but having the door unlocked means that they would then have to return later. It is more likely that the speakers have already left the door and they have realised that the door has not been locked and so now, they have to return. In which case the sentence would need changing slightly I forgot to lock the door we’ll have to GO back

Knock is what you do on a door when you want to get someones attention. Or it can be a slight bump, usually without great significance. E.g. I took a bit of a knock whilst playing football. Thump is usually a harder type of knock. It can be used instead of "punch". He gave me a big thump on the arm. Or it can be used to demonstrate that some force is being used in knocking. He thumped on the door to get attention.