There are probably other correct answers, but trio works: YEL055C, YLR175W, and YDR211W. If you set the desired threshold at 0.6, you get a single cluster.
To see the clustering history, click on “Stepwise Clustering History” to see this report:
Step 1: YLR175W clustered with YDR211W, correlation = 0.950293370931467
Step 2: YEL055C clustered with YLR175W::YDR211W, correlation = 0.705534919213607
If you sent the threshold for 0.9, you get two clusters:
Cluster 1: YEL055C
Cluster 2: YLR175W - YDR211W
The graph is unchanged.