A Task on the SAT Writing

A change in the insect population could have a disastrous impact on 1 certain bird species. They rely on the affected insects as their food source. 1. Which choice most effectively combines the sentences at the underlined portion? A) NO CHANGE B) certain bird species that rely on the affected insects C) certain bird species relying on the affected insects D) certain bird species, and they rely on the affected insects I thought that the answer is the "C" answer choice. It is both the most concise and grammatically correct. It turned out that the "C" answer choice is incorrect. The "B" answer choice is correct. I understand it is also grammatically correct and not so long, but, anyway, it is longer than the "C" one. On the SAT we must choose grammatically correct and the most concise answers. What is wrong with the "C" one then?