In order to fill in the blank with the correct form of the verb, let's understand the tense of the sentence.
The words 'since seven years' explain to us that the action started in the past and is still continuing in the present, and is unfinished. Hence, we must use present perfect continuous tense.
Option B - 'Have learned' is the present perfect tense. Here the action is completed. The given sentence states that the action is still continuing. Hence, option B is incorrect.
Option C - 'Have learnt' is grammatically not correct as we use the third form/past participle form of the verb with 'have' to form present perfect tense. As we need the present perfect continuous tense, we can't use 'have learnt'. Hence, option C is incorrect.
Option D - 'Learned' is the past form of the verb 'learn', which is used when the action is completed. Hence, option D is incorrect.
Option A - 'Have been learning' can be used here, as the words have been' explain to us that the action started in the past and the participle form 'learning' explains to us that the action is continuing in the present and is unfinished. Hence, option A is the correct answer.
'I have been learning English for seven years.'