관계대명사 계속적용법 질문이요~

안녕하세요. 관계대명사 계속적용법에 대해서 질문을 드립니다.인터넷수능-영어독해연습 b형 8강 4번 문항입니다.today, america’s charitable spirit remains strong as seen in giving usa, the yearbook published by the giving usa foundation. according to the 2008 issue of giving usa, american giving reached a record high, $306.39 billion for 2007. ① religious organizations received the largest share, with about a third of all contributions. ②educational institutions received the second largest percentage, with about 14 percent of the total contributions. ③ the contributions to human service organizations accounted for 9.7 percent, which was a slightly larger share than that of foundations. ④ donations to arts, culture, and humanities groups were 13.67 billion dollars, which was a bit smaller than those to international affairs groups. ⑤ the contributions benefiting the environment and animals were relatively small, accounting for about 2.3 percent.

여기서the contributions to human service organizations accounted for 9.7 percent, which was a slightly larger share than that of foundations.굵은 부분에서요, 계속적용법이 쓰인 것 맞죠?그러면 여기서 was인 이유는 무엇인가요? which가 contributions 를 지칭하는데, 여기서는 수의 일치는 시키지 않나요?? 질문드립니다 ㅜㅜ