Given the findings in the passage, which additional result most strongly indicates that the TGFBR1 and TGFBR2 receptors regulate TGFβ-dependent epithelial proliferation?

Answer: Option B.

Explanation:

The first experiment of the passage shows that treatment with TGFBR1 and TGFBR2 antagonists led to lower levels of epithelial cell production. For this conclusion to be strongly valid, we want to show a positive correlation between TGFBR activity and epithelial proliferation.