C.
Explanation: Because mirrors are lighter, and they are easier than lenses to make perfectly smooth.
Then the force of gravity between them would be quadrupled and so on but the gravitational force is inversely proportional to the square of the separation distance between the two interacting objects which makes more separation distance will result in weaker gravitational forces
The answer of question 1 is:
C. The gravitational force becomes 16 times less.
The answer of question 2 is:
A. The gravitational force is 12 times larger.
The answer of question 3 is :
A. The new gravitational force is 9 times stronger than the old one.
The answer of question 4 is:
D. 8 times more.