Hmm. Just checked again. Two of the expressions match neither word, one matches both, and one matches only one.
EDIT: I see. The confusion is over partial match vs whole match. I thought whole matches were standard when talking about regular expression in the abstract, but looks like I was wrong. Just changed the problem to include the anchors. Thanks for pointing this out.
That's not the standard meaning in my experience. Regex's are often used for extracting information from larger strings, forcing a full match by default would be pretty counter to their purpose.
EDIT: I see. The confusion is over partial match vs whole match. I thought whole matches were standard when talking about regular expression in the abstract, but looks like I was wrong. Just changed the problem to include the anchors. Thanks for pointing this out.