Detailed Instructions: In this task, you are given two sentences in the English language (Sentence 1 and Sentence 2). Your task is to identify the connecting word between the two sentences.
Q: Sentence 1:The D and D receptors have a high degree of structural homology and few ligands are available that can distinguish between them as yet . Sentence 2:However , there is a number of ligands that are selective for D over the other dopamine receptors .
A:
however