Because a liquid can take the wheight of the hydraulic press while a gas could combust under pressure.
(a) 
<u>Explanation:</u>
Given:
Moment of Inertia of m₁ about the axis, I₁ = m₁x²
Moment of Inertia of m₂ about the axis. I₂ = m₂ (L - x)²
Kinetic energy is rotational.
Total kinetic energy is 
Work done is change in kinetic energy.
To minimize E, differentiate wrt x and equate to zero.

Alternatively, work done is minimum when the axis passes through the center of mass.
Center of mass is at 
Answer:
Materials which do conduct electricity, like copper, are called conductors. In the middle are materials known as semiconductors, which don't conduct as well as conductors, but can carry current.
I hope it helped you...
This question is personal preference... just answer with whatever YOU think, there probably isn’t s wrong answer if I’d guess.