Significance of 'does' -- Where it comes in to the usage?

[Semen]

Business English Courses, Elementary Level

ESL/EFL Test #42 "Basic Business English", question 9

Yesterday they ......... very well in their class.

(a) do
(b) does
(c) will do
(d) did

Business English Courses, Elementary Level

ESL/EFL Test #42 "Basic Business English", answer 9

Yesterday they did very well in their class.

Correct answer: (d) did

Your answer was: incorrect
Yesterday they does very well in their class.
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could you please explain the significance of "does"?
where it comes in to the usage?

Semen

[Mister Micawber]

.
Here it is used idiomatically. To do well = to succeed; to perform satisfactorily.

Do is also called an operator, because it operates with main verbs to create:

Questions: Did you see him?
Negatives: I did not (didn't) see him.
Emphasis: I did see him on Tuesday, though.

It is also a main verb:

I did the laundry.
I did my homework.

But I think your question is about does. Does is the third person singular present simple tense of the verb:

He does his homework every day.
Does he take time off to play?
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber