In contest, which is the best way to revise and combine the underlined portions of sentences 14 and 15 (reproduced below)? Prinstein explains that teenagers use cliques to categorize their peers. (15) He further says that they use the cliques when they move on to middle or high school, where student populations can reach the thousands.

Direction for questions 7 to 12: The following passage is an early draft of an essay. Some parts of the passage need to be rewritten. Read the passage and select the best answers for the questions that follow. Some questions are about particular sentences or parts of sentences and ask you to improve sentence structure or word choice. Other questions ask you to consider organization and development. In choosing answers, follow the requirements of standard written English.

Passage – II
(1) “When kids are tossed together everyday, six hours a day for the entire school year,” says psychologist Thomas J. Berdnt, “friendship groupings form quite naturally. (2) ”These“ friendship groupings,” better known as cliques, are small, tightly knit, autonomous, and sometimes inclusive groups of people that share the same interests or characteristics.(3) Members of cliques often share the same values and exhibit the same behavior. (4) They have been known to form in elementary school, cliques are commonly associated with middle and high school students.
(5) In a recent nationwide survey of teenage girls’ views of cliques, 96.3 percent of the  claimed that cliques existed in their schools. (6) In addition, 84.2 percent of the respondents reported that most of their classmates belonged to cliques.
(7) Cliques “can be based on appearance, athletic ability, academic achievement, social or economic status, talent, ability to attract the opposite sex, or seeming sophistication,” according to adolescent development experts Anita Gurian and Alice Pope.(8) The prominent characteristic of a clique usually becomes the clique’s label. (9) A group of self-assured, varsity-jacketed male students might be known as “jocks” while another group’s unkempt appearance and spacey demeanor could earn them the “stoner” or “druggie” label. (10) While every high school in America seems to have its own “jocks,” “stoners,” or “druggies,” cliques can become well defined and evolve based on a school’s particular environment and culture.
(11) There are strong incentives for adolescents to join cliques.(12) For example, teenagers use cliques to ease their way through large peer groups. (13) Psychiatry professor Mitch Prinstein claims that cliques are a “sort of shortcut for adolescents to develop friendships and romantic relationships.” (14) Prinstein explains that teenagers use cliques to categorize their peers. (15) He further says that they use the cliques when they move on to middle or high school, where student populations can reach the thousands.(16) Cliques and peer groups also help them establish an identity.(17) Importantly most, teenagers join cliques to gain a sense of belonging.