Question

my classmates___on picnic every month.
1. went
2.goes
3.going
4.go

Answer 1

My classmate go on picnic every month.

Answer 2

Hey!!
Thanks for the question!!

Here is the answer..

My classmates $\textbf{go}$ on picnic every month.
_________________________
This is the answer.

$\text{Always remember..}$

As the sentence is in present tense, and there is no article then you cannot use verbs like went / going.
Also, you cannot use the verb 'goes' here because the noun is in plural form.
Hence, only 'go' suits the sentence.

I hope my answer helped!!

Thanks!!

#BeBrainly!