Read the following paragraph. How does sentence 4 develop the main idea of the paragraph?

Gertrude Belle Elion was born on Jan. 23, 1918, in New York City.
She graduated from Hunter College in New York City with a degree in biochemistry in 1937.
Unable to obtain a graduate research position because she was a woman, she took a series of jobs, including lab assistant, chemistry and physics teacher in New York City high schools, and research chemist.
During this time she also took classes at New York University, where she earned a master's degree in 1941.
Because she could not devote herself to full-time studies, Elion never received a doctorate.
This sentence tells readers where she went to school for her doctorate degree.
This sentence shows Elion's determination and commitment to learn.
This sentence shows that Elion had to try many schools to get accepted into one.
This sentence proves the idea that Elion had to learn biochemistry in unusual ways.