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题库 / Prep2007E2-SC-91
The spectacular disintegration of a comet last year in full view of ground- and space-based telescopes provided new insights into how comets form and may thus force a rethinking of the role of comets in the delivery of organic compounds to the evolving Earth.
The spectacular disintegration of a comet last year in full view of ground- and space-based telescopes provided new insights into how comets form and may thus force
The spectacular disintegration of a comet last year in full view of ground- as well as space-based telescopes, provided new insights into how comets form and thus possibly forcing
When a comet's spectacular disintegration occurred in full view of ground- and space-based telescopes last year, it provided new insights into how comets form and thus may possibly force
Last year, in full view of ground- and space-based telescopes, a comet's spectacular disintegration provided new insights into how comets form and thus possibly forcing
Last year, in full view of ground- as well as space-based telescopes, the spectacular disintegration of a comet has provided new insights into how comets form and may thus force
PAST TENSE vs. PRESENT PERFECT TENSE
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The PAST tense is used for:
* HISTORICAL ACTIONS
Ex: Mexico achieved independence in 1810.
* POINT ACTIONS that do not have a direct bearing on the current situation
Ex: Thomas, who is the president of First National Bank, won two Olympic medals in track
and field.
* ENDURING ACTIONS/STATES that are FINISHED
Andrea was the president of First National Bank from 1990 to 1994.
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The PRESENT PERFECT is used for:
* POINT ACTIONS that DO have a direct bearing on the current situation
EX: Thomas, who is the fastest sprinter in his country’s history, has won two Olympic medals
in track and field.
* ENDURING ACTIONS/STATES that are STILL ONGOING
Carlos has been the president of First National Bank since 2001.
Note that, in some cases, the same point action could be described either by the past tense or by the present perfect tense!
(See the two examples with "Thomas" above.)
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