Scientists have recently ................. research on blood lead levels of ...

[ Phrasal Verbs ]

Scientists have recently …………….. research on blood lead levels of athletes.

A. carried out

B. found out

C. narrowed down

D. resort to

Select your answer:

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Present Perfect or Past Simple Tense Grammar and Passive Voice Phrases & Clauses Subordination Conjunctions Quantifiers and Adjectives Modal Verb Simple Present & Present Progressive Past Perfect Simple & Continuous Modals and Past Modals

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A. Why；Because

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