Seeds that are transported by wind or water typically are
a. dispersed by animals.
b. lightweight.
c. large.
d. sweet and fleshy.

Option B, lightweight

Explanation:

Wind basically carries away the seeds which are light weight and winged which makes them peculiar to fit in the criteria required for floating. For example seeds of swan plants and cotton wood are light weight and also have some feather like bristles which allow them to be carried away by wind to a longer distance.

Water also carries light weight seeds as they can easily float on the water  for example seeds of mangrove trees.  

Thus, Option B is the correct answer