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 ("<em>more than all of the earth plants and trees combined</em>"), different from the other option (D) which goes straight to the point thorugh the use of a simple sentence.
Cathedrals in the middle ages were typically large churches and were considered the center church of the bishop's throne. In the medieval times, monumental cathedrals were built to symbolize of faith and a display of creativity within the middle ages society in Europe.
“The United States should help free nations resist the spread of communism” best describes a belief held by President Truman that led to the establishment of the Truman Doctrine.
The Truman doctrine’s main purpose is for the United States to help in opposing the spread communist ideals around the world.
