Scientific Discovery
Present Perfect vs. Past Simple: NASA's Curiosity rover (find) liquid water on Mars since it (start) a mission in 2012.
Has found / started
Present Perfect vs. Past Simple: TikTok (become) the world's favorite app since it (launch) globally a few years ago.
Has become / launched
Present Perfect vs. Past Simple: I never (eat) fried insects, but my cousin (try) them on his trip to Thailand last summer.
Have never eaten / tried
Present Perfect vs. Past Simple: Since the UK (leave) the European Union in 2020, many political leaders (debate) the long-term impact of Brexit on continental trade.
Left / have debated
Present Perfect vs. Past Simple: Taylor Swift (break) dozens of records since she (begin) re-recording her "Taylor’s Version" albums.
Has broken / began
Present Perfect vs. Past Simple: Since this year began, marine biologists already (identify) three new glowing shark species. They (photograph) them in the deep sea in January.
Have identified / photographed
Present Perfect vs. Past Simple: Engineers (build) the first VR headsets in the 1960s, but they only (have) 4K graphics since 2017.
Built / Have had
Present Perfect vs. Past Simple: Our school’s esports team (win) the trophy last week, and they (celebrate) their victory ever since.
Won / has celebrated
Present Perfect vs. Past Simple: Robots (collect) the first photos of the surface in 1976. Since the 1970s, humans (send) many robots to Mars to extract more data.
Collected / have sent
Present Perfect vs. Past Simple: The band BTS (perform) at the Grammys in 2020 and (stay) at the top of the charts since then.
Performed / has stayed
Present Perfect vs. Past Simple: In 1953, researchers (map) the DNA helix for the first time by studying X-Ray images. However, scientists (not yet understand) the meaning behind every sequence of DNA.
Mapped / have not yet understood
Present Perfect vs. Past Simple: Since 2009, Bitcoin (change) finance and created new wealth. The value of 1 BTC (reach) a historic high of $126,000 in October of 2025.
Has changed / reached
Present Perfect vs. Past Simple: My sister (meet) three famous YouTubers since she (move) to Los Angeles in September.
Has met / moved
Past Perfect vs. Past Simple: By the time the Vikings (reach) North America, they already (cross) the freezing ocean in open boats.
Reached / had already
Present Perfect vs. Past Simple: In 1997, the movie Titanic (earn) billions of dollars and (win) eleven Academy Awards. The lead actress, Kate Winslet, (star) in many movies since then.
Earned / won / has starred
Past Perfect vs. Past Simple: By the time the asteroid (hit) Earth, the dinosaurs (rule) the planet for over 150 million years.
Hit / had ruled
Past Perfect vs. Past Simple: Before the first iPhone (arrive) in 2007, most teens (never use) a touchscreen device.
Arrived / had never used
Past Perfect vs. Past Simple: I (realize) I (leave) my phone in the Uber only after the driver pulled away from the curb.
Realized / had left
Past Perfect vs. Past Simple: Before builders (finish) the Great Wall, Chinese dynasties (work) on it for over 2,000 years.
Finished / had worked
Past Perfect vs. Past Simple: The singer already (write) the lyrics to the hit song before he (turn) sixteen years old.
Had already written / turned
Before the team (open) the ancient tomb, they already (use) high-tech scanners to see the gold inside.
Open / had already used
Past Perfect vs. Past Simple: By the time Microsoft (buy) the game, the creator of Minecraft (already earn) millions of dollars.
Bought / had already earned
Past Perfect vs. Past Simple: She (practice) that difficult skate trick for three months before she finally (land) it perfectly.
Had practiced / landed
Present Perfect vs. Past Simple: Pedro Alvares Cabral (arrive) on the coast of Brazil in 1500. Ever since his arrival, the blend of indigenous, African, and European cultures (shape) Brazil’s unique national identity.
Arrived / has shaped
Past Perfect vs. Past Simple: By the time the concert finally (start), the fans (wait) in the pouring rain for six hours.
Started / had waited