Help understanding a particular LR question Forum

[cgomez]

Mature white pines intercept almost all the sunlight that shines on them. they leave a deep litter that dries readily, and they grow to prodigious height so that, even when there are large gaps in a stand of such trees, little light reaches the forest floor. For this reason white pines cannot regenerate in their own shade. Thus, when in a dense forest a stand of trees consists of nothing but mature white pines it is a fair bet that___.

Which one of the following most logically concludes the argument?

Answer: A. the ages of the trees in the stand do not differ from each other by much more than the length of time it takes a white pine to grow to maturity.

I was able to get the right answer by eliminating the others, however I still do not understand the reasoning. More specifically, how the statement leads logically to this particular answer.

Thanks! sorry if i'm too vague.

[Tiago Splitter]

Because if some of the white pines grew to maturity before the others, their shade would crowd out the other newly growing white pines. Those new ones would then be unable to grow.