The word "cotyledon" refers to the of an angiosperm
A. seed B. shell

Neither technically

Explanation:

A cotyledon is the first leaves of the plant. The first leaves, even though they are not true leaves. But, in this case since there are only two choices, I would have to say A) seed because the cotyledons are inside the embryo of the seed. If there is another answer, than it would be the first leaves that pop out of the soil. Their purpose is to gather sunlight and strength for the plant, so it can produce the first true leaves. After the true leaves grow out, the embryonic leaves (first leaves) will wither away, and eventually fall off. Good luck!!