Scratching my head on this one

[sparkydave]

I've been looking at the playgo.to site, and learned a few things. I must be learning something, I managed to beat my smartphone finally. There's one problem on this page that I have given up on, it's #2. I found two of the moves that seem to work (E2 and C1), but I can't seem to find the third move. I thought E1 would have been the logical one, but I can't seem to get past it.

http://www.playgo.to/interactive/complex.html

Any ideas?

[illluck]

C1 is not right. A hint is the response to C1.

[sparkydave]

Aha! Thanks for the tip! Correct moves are E2, C5, and D5. Little by little, I'm learning. Thanks much!