The correct option is B had been recording
The past perfect continuous form of any verb is obtained by adding 'had been' to the base verb + ing. The verb in question is 'to record'; for which the base/ root form is simply 'record'. Applying the above, we clearly get 'had been recording', which is Option B) - the correct answer. A) is simply past continuous tense; C) is past tense, and D) is simple past tense as well.