Analyze the following statements regarding the use and functions of English verb tenses:

I- In the sentence “I have been writing this report all morning,” the Present Perfect Continuous is used to emphasize the duration and the ongoing nature of the activity leading up to the present moment.
II- The Future Perfect (will have + past participle) is correctly employed to describe an action that will be completed at or before a specific point of time in the future.
III- The Past Simple and the Past Continuous can be used together in a single sentence to indicate that a longer background action was interrupted by a shorter, discrete event.
IV- The “State Verbs” (or stative verbs) like know, believe, and belong are frequently used in continuous forms to indicate a temporary state of mind.

Which of the statements above are CORRECT?