I believe the answer to this question is D. correct as is.
Vashti made a dot without painting by using a pen or pencil, tears or blood. Dots can be made by nearly anything, glue, chalk, yet just no paint.
To see Mercury with your naked eye is only possible when it is at its greatest "elongation" or basically when the angle of separation between the Sun or Mercury is at it's greatest value, however it is not always a promised success of viewing Mercury. It also depends on the phase of the plant to determine how bright it is!
