What does keep it down mean?

[Hella]

English Language Tests, Intermediate level

ESL/EFL Test #517 "English Slang Idioms (259)", question 4

"I know that it is summer time and it's light outside until late but you two are going to have to keep it ......... out here while you are playing. A lot of the people who live closeby have to wake up really early to go to work and they can't sleep with you two screaming and yelling until all hours of the night," Allen told his two boys.

(a) away
(b) down
(c) up
(d) closed

English Language Tests, Intermediate level

ESL/EFL Test #517 "English Slang Idioms (259)", answer 4

"I know that it is summer time and it's light outside until late but you two are going to have to keep it down out here while you are playing. A lot of the people who live closeby have to wake up really early to go to work and they can't sleep with you two screaming and yelling until all hours of the night," Allen told his two boys.

Correct answer: (b) down
_________________________

what's the meaning of "to keep it down"? Maybe something like "keep quiet"?

Hella

[Benjamin]

yes
if you tell someone to keep it down then yes, you are basically telling them to be quiet. it might be a more polite way of saying it.

the "it" in "keep it down" refers to the "noise level"