Choose the answer that best completes the sentence. Americans are closer today to fulfilling America's promise of economic and social justice; , America's future progress will depend on how Americans prepare their next generation of leaders,
A. however
B. therefore
C. because
D. whenever

A however

Explanation:

A. however is the answer

You can simply go to the website
PubMed.gov
Type in the words
Irritable bowel syndrome 
Go through the results and pick out the one you think is the most related.
This is one article that I think is related to what you're looking for:
"New insights into the pathogenesis and treatment of irritable bowel syndrome."This is the link: https://www.ncbi.nlm.nih.gov/pubmed/28135659