The potential must be strong enough to send a(n) potential to the cns.

The correct answer to the question above is action. The potential must be strong enough to send an action potential to the CNS (Central Nervous System.) An action potential is a short-term event that causes the electrical potential of a cell. 

The plants that produce a seed without a protective cover are known as Gymnosperms.
Gymnosperms have no fruits (protective cover), and they have unenclosed or “naked” seeds on the surface of scales or leaves. Their seeds are often called cones. Another difference from Angiosperms (with enclosed seed) is that they don’t have cotyledons  and that their endosperm is haploid