In the following text, what type of connector best fits in the blank to logically connect the ideas?

To understand microbial patterns associated with child growth, the researchers sequenced the genomic material from 47 fecal samples collected over 11 months from eight toddlers, who had (      ) been enrolled in a clinical trial testing the effect of legume-based complementary foods on reducing or reversing environmental enteric dysfunction, a chronic condition that affects the small intestine, and poor growth.