TOEFL Reading: ETS-TOEFL阅读机经 - 0R3KO9E77ME1LS50L$

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Any life forms that may have existed on other planets probably were destroyed by UV radiation. B. Other planets in our solar system lack the oxygen atmosphere that helps explain why life exists on Earth. C. The absence of oxygen on other planets means that those planets lack an ozone shield to protect life forms against UV radiation. D. Life forms cannot survive UV radiation without the protection of an ozone shield.