English Grammar

Sorry to tell you that all of the four sentences are incorrect!!

Cuddle (as verb) Dawn and her boyfriend were cuddling on the sofa.
Cuddle up: The children cuddled up to each other for warth.
Cuddle (as noun): an act of cuddling someone.
The above 3 examples are from Longman Dictionary of Contemporary English.

I saw him standing there!!!

You should use past tense as they were cuddling while you SAW (當你看見一件事情時，那時情是已發生了，是你看見，已看見，所以應用過去式，而在你看到的時候，他／她們卻在進行中，但卻形容他／她們在做什麼，所以將cuddle 攺為cuddling，就如以上那example, Dawn and her boyfriend were CUDDLING on the sofa.

正確的答案是: I saw them cuddling up........

Injure (as verb): to cause physical harm to someone or to yourself.
Injured (as adjective): having injury.......
Injury (as noun): a woundor damage to part of your body caused by an accident or attack.......

A day before? what do you mean to say that? 一日前是某一日之前還是沒指定那一日? 英文應該沒有這樣說．
如是一日前受傷，便會說: He was injured yestday.
如是說一日前有傷便會說: He had an injury during the sports on last Sunday.
若指定那一天愛傷，便會說: He was injured on Monday(Tuesday.........last Saturday....etc.)
若說在指定某一天有傷便會說: He had an injury during the car accident on Tuesday.

If you want to point out the injury and the day, you need to make it clear why and when happened.

P.S. ilee, him or her 雖然是第三身單數，但那不是要在你那個句子的動詞加 s 理由

1) I see him cruddle up, definitely,it's wrong.
him is the 3rd person single, so the verb following it should have added an 's'.
Therefore, I see him cruddleS up is then correct. I see him CRUDDLE up is wrong____

I see him cruddling up is correct.
the reason is that, 'he is cruddling up' is 發生ing, so we say 'i see him cruddling up'__

2) please pay attention to the word 'injure' ....injure means 傷害(某人), it is an ACTIVE VERB. He had injured a day before=幾天前，他傷害了。it's imcomplete.
He had been injured a day before.=幾天前，他被傷害了。(被傷害，繹的好d，就是受了傷)it's completed and it's absolutely correct~

I see him cuddle up
He had been injured a day before

1.I see him cuddle up .......
see後面好似係用bare infinitive架。

2. He had been injured a day before.
呢個係passive voice，即係被動形式，他被傷了。

I see him cuddle up is correct
He had been injured a day before.