At low temperatures, long-chain polymers are usually ________.

A) glasses
B) thermoplastics
C) highly cross-linked
D) very flexible
E) gummy

At low temperatures, long-chain polymers tend to become very rigid and brittle, making them behave like a glass rather than a flexible material. This is due to the decreased mobility of the polymer chains at lower temperatures. Therefore, the best choice for this question is A, glasses.