Choose the sentence in which the verb is a linking verb
> he has walked to work form his house
> his boss pays him well
> he works at a gas station
> his hours are long and busy

The sentence in which the verb is a linking verb is letter D: His hours are long and busy.  

Verbs are simply known as the ‘action’ words – may it be mental, physical or mechanical. When verbs are paired with auxiliaries (helping verbs), they are known as verb phrase.

These helping verbs always go first before the actual verb.   Perfect tenses serves a portraying the verb or the action word as something that already happened or is completed, thus the term ‘perfect’. If it is present perfect tense, it means that the action was already done relatively to the present (has/have with past participle). If it is past perfect tense, action is already finished relatively to the past (had with past participle and if it is future perfect tense, action is complete relatively to the future (will have with past participle).