My gratitudes to my teachers....

I hope you answer the questions I am still struggling on.

Question 1.

In a movie, a pilot gets hit on his plane, and takes a landing in some place he doesn't know where.

At last, the pilot happens to meet two soldiers, not the rescue team but just the allied force.

So, the pilot asks them, "Why there's only two of you?"

The pilot is mistaking that the two soldiers are his rescue team.

In that situation, is the sentence, "Why there's only two of you?" correct?

How about this logic? Because the soldiers were TWO, than the pilot should have said, "Why there ARE only two of you?"

Question 2.

After the words, "the trousers, the pants, the scissors, the glasses....", the words meaning a pair, should the verb be plural or singular?

The pair of trousers that you just bought IS good. ......... or, The pair of trousers that you just bought ARE good.

Which is the correct native's sense of English?
Hm, the first one is a doozy. I'll just do the second one:

A pair of trousers is something.
Trousers are something.

Remember that in the first example, you are talking about the pair, not the things that comprise the pair. (People who claim to be writers get this wrong all the time, especially in music literature, when people say things like "Radiohead are Thom Yorke, Jonny Greenwood, Colin Greenwood, Ed O'Briend, and Phil Selway." Of course members of a band are many, but the band itself is singular.)

Another maddening question is: who ever heard of a trouser?
Actually, I think you are right about the first one: it is grammatically incorrect to say "why there's only two of you." First of all, it should be either "why, there's only two of you!" or "why is there only two of you?" The next step to making this sentece correct is, as you suggest, to make the verb plural to reflect the number of the subjects: "Why, there are only two of you!" or "why are there only two of you?"
Students: We have free audio pronunciation exercises.
Thanks, Mr. TimKowal!