Hello Joo!

Great questions! Let's see if I can help.

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In #2 on the 'Module 2-1 Sentences' section,
the answer is 'The janitor found the lost key under a pile of papers about to be thrown away.'
I'm assuming 'that were' between 'papers' and 'about' might have been omitted, and I was wondering
when I can omit 'that were' in other sentences.


-> First, it was probably "that was" that's omitted, not "that were" since it's "a" pile of paper(s).

To answer your question, it really depends on the context. One rule is your sentence should be very clear even without the omission.

For instance,

"I have a meeting with Mason who is about to fly back to Canada on Friday."

Here it's probably not a good idea to omit "who is" because...

"I have a meeting with Mason, about to fly back to Canada on Friday."

now it is vague if it's you or Mason that's flying back to Canada on Friday.


Another (awesome) example,

"Students were happy happy to see Mason, the best teacher in the world."

"Students were happy happy to see Mason who is the best teacher in the world."

Here, it's very clear to see that it's Mason who is the best teacher even without "who is"

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In #10 on 'Module 2-1 Sentences' section,
the answer is '~ in the next few hours' or '~for a few hours,' while I translated it as 'in a few hours'.
I am confused about the usage of prepositions.


-> Usages of prepositions are tricky. It takes a lot of reading/writing/listening to really acquire it so do not worry you are struggling, because every does and I do very often.

One reason why you wouldn't say "in a few hours" is because the sentence has a negative connotation. If you wanted to say "손님들은 몇 시간 후면 도착할 것 같다" I think you could say "It seems customers will arrive in a few hours." That would be fine. I think Grace had explained very well in the video, so I suggest you to watch once again if you are still not clear!


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In #2 on 'Module 2-2 K to E Passages' section,
the translation for '편리함에 있어서 비행기는 헬리콥터를 따라가지 못 한다' is
'In convenience, airplanes cannot compare to helicopters.'
I wondered why it is not translated in a passive voice because 'airplanes' cannot DO something.


-> Short answer: You are right, but the passive voice rule thing doesn't REALLY matter that much often.

Although I do agree that you could say "airplanes cannot be compared to helicopters" instead,

I don't think it really causes a significant problem. In fact, this happens more than often in real life.

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I hope my answers help!

- Mason (Instructor)