TOEFL Reading: ETS-TOEFL阅读机经 - 6E3JWCL_O3GV156VL$

It can be inferred from paragraph 5 that early life-forms on Earth were confined to the oceans because A. the thick ozone layer at the time would have made it difficult for them to survive on land B. water was the only available protection they had against ultraviolet radiation C. land provided them with only limited amounts of water needed for survival D. their metabolic systems were inefficient