John _____ (study) for two hours.

Correct option is D

• A) Was studying: This past continuous tense is incorrect because it suggests the action was happening in the past but doesn't indicate it's still ongoing.

• B) Studied: This simple past tense is incorrect because it suggests the action was completed in the past.

• C) Had studied: This past perfect tense is incorrect because it suggests the action was completed before another action in the past.

• D) Has been studying: This present perfect continuous tense is correct because it indicates that the action started in the past and continues up to the present.