Pieces of metal flashing longer than 10 feet can be a problem because:

Long sections of metal flashing exceeding 10 feet can indeed be prone to buckling due to temperature fluctuations. Metal expands when it heats up and contracts when it cools down. When long pieces are installed, this expansion and contraction can create stress, leading to buckling if there isn't enough room for movement. This is particularly important in roofing and siding applications, where the integrity of the flashing is essential to prevent water intrusion.

While the other choices may relate to some aspects of installation, they do not directly address the specific issue of buckling caused by the physical properties of metal. Buckling is a critical concern that can undermine the effectiveness of flashing and lead to significant problems down the line, such as leaks or structural damage.