This is a question of units ... you have to
go through the list and find the choice that
has units of mass.
The first one (A) is the only one that has.
The ' g ' stands for 'gram', a unit of mass.
The other choices have units of
-- lb . . . pound, a unit of force
-- n . . . Newton, another unit of force
-- m . . . meter, a unit of length or distance
