Final answer:
The Present Perfect Continuous tense, represented by 'They have been studying for several hours,' is the correct choice to express an action that started in the past and continues into the present.
Step-by-step explanation:
The appropriate verb tense to show an action that started in the past and continues into the present is the Present Perfect Continuous tense. This tense is used to describe actions that began in the past and are still ongoing in the present moment. Among the options provided, the correct choice is B: Present Perfect tense, exemplified by the sentence 'They have been studying for several hours.'
The Present Perfect Continuous tense, also known as Present Perfect Progressive, combines the present tense of the auxiliary verb to have ('have' or 'has') with been (the past participle of to be) and the -ing form of the main verb. This structure emphasizes the duration of the activity that is still happening. Other tenses provided in the options, such as Future Perfect, Past Perfect, and Present tense, are not suitable to express actions initiated in the past but continuing in the present.