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? ['other species of trees will soon begin to colonize the stand, eventually replacing all of the white pines', "competition among the trees in the stand for sunlight will soon result in some trees' dying and the stand thus becoming thinner", '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', 'the land on which the stand is now growing had been cleared of all trees at the time when the first of the white pines started growing']