Identify the tense of the following sentence:"He had been riding a bike since 8am."

The tense of the sentence "He had been riding a bike since 8am." is Past Perfect Continuous.

Here's the step by step identification:

1. Look for the verb in the sentence: The verb here is "had been riding".

2. Identify the form of the verb: The verb "had been riding" is in the past participle form with the auxiliary verbs "had been" which indicates a continuous action.

3. Determine the tense: Since the action was ongoing in the past, it is in the Past Perfect Continuous tense. This tense is used to show that an ongoing action in the past has ended.