Seal.
The verb in the sentence is "had been." This is a compound past perfect verb form indicating that the hook was not properly baited at a specific point in the past.
The simple predicate of the sentence "Is a walrus a type of seal?" is "is." The simple predicate consists of the main verb or verb phrase that expresses the action or state of being in the sentence. In this case, it indicates the state of being regarding whether a walrus belongs to the category of seals.
In the sentence "The trained seal balanced a ball on its nose," the predicate is "balanced a ball on its nose." The predicate includes the verb "balanced" and provides information about what the subject (the trained seal) is doing.
He needed to project his voice more if everyone at the back of the room were going to hear him properly.
A transitory (or, more properly, transitive) verb is an action verb which, according to conventional rules of grammar, must "take", or transition into, a direct object. "He rides the horse" is an example-sentence for the transitive verb, to ride.
The verb in the sentence "How are they different" is "are."
Is is the verb in your sentence.
This question needs more information to be able to answer it properly. The sentence would need to contain a noun, which is a person, place or thing, and a verb which is an action.
He needed to project his voice more if everyone at the back of the room were going to hear him properly.
The verb in that sentence is "are".
Were is the verb in that sentence.
I think the linking verb is should. Have is the helping verb and should links it into the sentence properly.