Question

A. pair of scissors _____ in the cupboard

Answer 1

Hey there!  

The answer to your question of filling the blank with a required helping verb is " is "

                      A pair of scissors is in the cupboard.

• When we say a pair of scissors, we mean  a single pair of scissors.
• Though there is a pair  it's still considered as single .
• As there is no mention about the tense of the sentence, we consider it to be present.
• For singular object, We use “is”
• Therefore, The required sentence is “ A pair of scissors is in the cupboard ”

Hope helped!

Answer 2

Pair of scissors is in the cupboard.

( pair of scissors) is a collective noun