What is the precise meaning of "alertly" in this excerpt from the chapter III of The Great Gatsby:
“Who brought you?” he demanded. “Or did you just come? I was brought. Most people were brought.”
Jordan looked at him alertly, cheerfully without answering.
In Chapter Three, Nick is one of the few people who have been invited to Gatsby's hedonistic party on his "blue lawn." After he ambles around for a while, he spots Jordan Baker and takes her "golden arm" and they traverse the lawn, but Jordan says the party is "much too polite" for her. So, they enter the house in order to find their host; however, after they enter a "high Gothic library," they encounter a heavy-set middle-aged man, who wears "owl-eyed spectacles" and stares at the bookshelves. This rather inebriated man marvels that Gatsby's books are real.
"It's a bonfide piece of printed matter. It fooled me....But what do you want? What do you expect?"
Suspiciously, he looks at Nick and Jordan and asks, "Who brought you?....Most people were brought." At this point, Jordan becomes alert; that is, she is intrigued with "Owl-Eyes." wondering what his connection is with another guest who must have brought him. Watching for something unusual, the jaded flapper hopes for something to arouse her curiosity and amuse her.
Here, the word alertly is used as an adverb. It is describing Jordan's reaction to the man's "somewhat" drunken ramblings about the books in the library, as well as his inqusitiveness regarding whether Jordan was brought to the party by another guest, or was actually invited. The word is used to explain Jordan's silent acknowledgement of the question, probably with raised eyebrows and bulged eyes, due to the man's intrusive inquiry.