<CENTER><B>WARNING: Reading May Be Hazardous To Your Health</B></CENTER> <P> The principal of Jill and Gwen's school promised to spend the morning on the roof if the kids read one thousand books during their reading marathon -- and they did! Now he's on the roof, and he's going to read an original science fiction story Gwen wrote. <P> But he could fall <I>off</I> the roof is he doesn't stop sneezing. Is it a coincidence that Gwen's story is about aliens who live on roofs and make humans sneeze? Fletcher knows that Gwen would never pull a dangerous practical joke just to make her story come try. But can he prove it before Gwen's in big trouble?