Identify the tense used in the sentence "I have been reading this book for a week."

The tense used in the sentence "I have been reading this book for a week" is the Present Perfect Continuous. This tense is formed using the present perfect of the verb "to be" (which is "have been") combined with the present participle of the main verb (in this case, "reading").

The Present Perfect Continuous tense emphasizes the duration of an activity that started in the past and continues to the present, or has recently stopped but still affects the current situation. The phrase "for a week" indicates that the action of reading began a week ago and is still ongoing. This aspect of the tense highlights both the continuity of the action and its relevance to the present moment, which is a key characteristic of the Present Perfect Continuous tense.

This understanding of the tense indicates not merely a completed action (as would be the case with other tenses) but rather the ongoing nature of the activity and its temporal context related to the present.