Which best revise this sentence for clarity without changing it overall meaning marin algae, the ocean plants life that generate more oxygen than all of earth's plants and trees combined' produce up to 80 percent of earth oxygen a. marine algae the ocean plants life that generate more oxygen than all the plants and tree that participate in photosynthesis produce up to 80 percent of earth oxygen b. marine algae produce 80 percent of earth oxygen the ocean plants life that generate more oxygen than all of earth plants and tree combine c. marine algae produce up 80 percent of earth oxygen - more than all of earth plants and tree combine d. marine algae produce up 80 percent of earth oxygen

The best answer is option C. This option is the one that includes the information given in the original sentence, but summarized (avoiding giving extra information about what marine algae are, or using complicated grammatical structures.)

Option D is quite short, but summarizes the main idea of the original sentence without giving any extra information at all.

None of these two options (C and D) change the overall meaning of the original sentence, but one of them (C) gives the reader more information about the points mentioned in the original sentence ("more than all of the earth plants and trees combined"), different from the other option (D) which goes straight to the point thorugh the use of a simple sentence.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).