我想問them 同 us 的分別

1. Dad said that we were good children and bought us a cake.
2. Sam and I got high marks in the exam, so Mum bought us presents.
them和us都係 object, 分別指他們和我們.
事情提及自己和某人所做既事就用我們, 若是提及一些人做既事而不包括自己在內就用他們呢!
eg. You and I are in the same school. The teachers teach us patiently.
Sam and Mary are free on Sunday. I call them to go outside.

we should use "us" for the two sentences.
if the sentence includes the subject " i" , we should use
me . if the sentence includes the subject " i and somebody",
we should use us.