Basic computer science knowledge (and yes, B-Trees qualifies) cannot be learned in 20 seconds. Most of this knowledge is actually a prerequisite to being able to search Google properly.
http://slady.net/java/bt/view.php?w=800&h=600 http://en.wikipedia.org/wiki/B-tree http://en.wikipedia.org/wiki/B%2B_tree http://guide.couchdb.org/draft/btree.html
Now if you make understanding B-trees a prerequisite for the job, I can at least learn it ahead of time for the position.
If you don't know about these data structures or algorithms, you won't even know where to look.