In which sentence is the word periscope used correctly?

Question

A. Excited about her finding, the scientist used a periscope to view the organisms in the water sample.
B. On the night of the full moon, we used the periscope to look at the sky.
C. Sitting behind the tall stone walls, the soldier used a periscope to view the field surrounding the fort. ***
D. I held the periscope up to the light and was delighted with the many patterns I saw!

Answer 1

c seems to be correct, yes.

Answer 2

Concave

Answer 3

Plane mirror