Answer:
- a.

- b.

- c.

Explanation:
The spacetime interval
is given by

please, be aware this is the definition for the signature ( + - - - ), for the signature (- + + + ) the spacetime interval is given by:
.
Lets work with the signature ( + - - - ), and, if needed in the other signature, we can multiply our interval by -1.
<h3>a.</h3>





so


<h3>b.</h3>





so


<h3>c.</h3>





so


supply it with more energy. one way to do is to produce vibrations in the same frequency as the wave. This would cause resonance leading to higher amplitude
no, work is = force * distance or displacement