The present perfect is a time span that includes now.

Source from NOAA

You can try thinking of the birds as discrete points of time and the waves as on-going aspects of a time span.

This video has the answers to these fill-ins. Thanks to Rachel's channel  (Archived ) and Voscreen.

- Scene 1: A: He's your uncle? B: Him? Uh-uh. I've ______________ seen him before. - Scene 2: ______________ never been sick before. - Scene 3: Hello darkness, my old friend. I've ______________ to talk with you again. - Scene 4: l've ______________ changes for you, Shrek. Think about that.

- Scene 5: A: How long ______________ he been gone? B: Two weeks, one day, 15 hours. - Scene 6: ______________ come to say good-bye. - Scene 7: Commuting to work by bike ______________ risen by about 60 percent in 10 years. - Scene 8: Alice has ________________. - Scene 9: I've ______________ a decision. We're going to that mountain. - Scene 10: Have you ______________ imagined a future with me? - Scene 11: My dream ______________ come true. Thank you. - Scene 12: The maniac Boov ______________ ruined everything. This is bad. - Scene 13: Their mother has not __________ for five months and has lost half of her body weight. - Scene 14: Something wonderful has ________________. Ani, I'm pregnant. - Scene 15: I've ______________ you so much.

Here are a few more interactive worksheets on the present perfect (“has spoken, have eaten”)

1. https://www.liveworksheets.com/w/en/english-second-language-esl/2170470 (Click on Finish rather than unintentionally clicking on the advertisements!)

2. https://www.englishclub.com/grammar/verb-tenses_present-perfect_quiz.php 

3. https://www.liveworksheets.com/w/en/english-second-language-esl/457943

4. https://elt.oup.com/student/solutions/preint/grammar/grammar_05_012e?cc=us&selLanguage=en  CORRECTION: Have they finished (they / FINISH) their homework yet?

Since - use the perfect (“have”) .

• “Since” is the dependent clause; “I’ve been on a diet" is the independent clause. An independent clause can also be a stand-alone sentence because it has a noun and verb.

• Spoken English allows the contraction "it's" for "it has"; written is evolving to allow one.
• https://langeek.co/en/grammar/course/741/because-vs-since
• The main difference between 'because' and 'since' is that 'because' only expresses reason while 'since' expresses reason and time.

1. I’ve been in this country since 2000.

1. I’ve been in this country since the year 2000.

2. I’ve been in this country since August of 2000.

3. I have been in this country since 2010.

2. I’ve been on a diet since January this year.
3. It has been more than six months since I’ve bought ice cream.

1. It has been more than six months since I bought ice cream.

2. I haven’t bought any ice cream in the last six months.

3. It’s been more than six months since I’ve bought ice cream.
   

See also

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https://grosslearning.blogspot.com/2024/03/the-present-perfect-is-time-span-that.html