Can someone pls help…


Does inflated balloon has elastic spring force?

Hi,

Need help for Booklet A CHIJ 2013 Prelims, Q20

There is a diagram shows some helium-filled balloons tie with string being released into the air.
As the balloons are rising,which of the following forces are acting on the balloons?

A) air resistance
B) magnetic force
C) gravitational force
D) elastic spring force

The ans is A,C and D.

I dont understand why D is the ans too?
I thought, elastic spring force only applicable to spring only?

Hi, 1st time here! My boy is in 1P1