Is it the same possibility that the yellow thumbtack is pointed up and pointed up?

There are three colors of traffic lights: red, green and yellow, but the time when the red, yellow and green lights appear is generally different.

They have different probabilities,

∴ think this is not an "equal possibility event",

∴ Option A is incorrect;

Thumbnails are different from top to bottom.

∴ The probability that the nail tip is facing up is different from the probability that the nail tip touches the ground.

∴ think this is not an "equal possibility event",

∴ Option B is incorrect;

The three sides of a right triangle are different in length.

∴ Liang Xiao is walking along three sides of a "right triangle", and the probability that he appears on each side is different.

∴ think this is not an "equal possibility event",

∴ option c is incorrect;

Xiao Ming randomly selects the above three answers, A, B and C are all the same.

∴ It belongs to "equal possibility event",

Option d is correct.

Therefore, choose: d.