For a court to determine that a contract is voidable on the basis of insanity, which one of the following is the correct statement of the law?

a$.$ The person seeking to prove capacity must prove that the insane person was of sound mind.

b$.$ The person seeking to prove incapacity must prove that the other person in the contract knew or ought to have known that there was a problem with mental capacity.

c$.$ The person seeking to prove incapacity must prove that he or she could not understand the nature of the contracting act.

d$.$ The person seeking to prove incapacity must prove that he or she lacked sound judgment.

e$.$ Contracts with insane persons are void, not voidable.