Answer:
D. Electrical charge
Explanation:
What actually caused the tissue paper to move towards the balloon is "electrical charge".
When they rubbed the balloon with a piece of wool, the wool looses electrons which gives it a positive charge while the balloon gains electrons which gives it a negative charge.
The pieces of tissue paper is able to move toward (i.e attracted) the balloon because the negatively charged balloon is attracted to the positively charged tissue paper which was neutral.
