Q: Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.
Problem: a father and his son are waiting at a bus stop in the evening. there is a lamp post behind them. the lamp post, the father and his son stand on the same straight line. the father observes that the shadows of his head and his son ' s head are incident at the same point on the ground. if the heights of the lamp post, the father and his son are 6 metres, 1.8 metres and 0.9 metres respectively, and the father is standing 2.1 metres away from the post, then how far ( in metres ) is the son standing from his father ?
Options: a. 0.9, b. 0.75, c. 0.6, d. 0.45, e. none of these
A:
d