Which sign are you not likely to see mounted beside the road?
a. no passing pennant.
b. slow-moving vehicle sign.
c. train crossing sign.
d. none of the above are correct

b. Slow-moving vehicle sign.

Explanation:

When driving there are many signs you must be aware of, one of these signs is the slow moving vehicle sign, which is a reflective triangle with its edges cut (shown below). This sign is used to warn other people that the vehicle is travelling in a slower speed than normal traffic (usually at 25 miles per hour at most). However, this sign hangs on the backside of the vehicle so the vehicles behind it can see it and reduce their speed.

Therefore, since this sign hangs on the back of the vehicle, it is not likely that you see it mounted beside the road.