I think including Euphonium (or baritone) makes complete sense, but including saxophone makes no sense at all..
They are considered part of a traditional orchestra, whereas guitars are not.
Edgard Varese is rolling over in his grave!
There are so many percussion instruments it is hard to think of them all.
We've got the bongos, guitar, saxophone, digeridoo, drums, banjo and a rainstick......
Didn't read the comments, so if nobody wrote it before - you should add "Contrabass" for Double bass :)
The bass trombone is very commonly used in large orchestral works from the late Romantic period and later.
My other quibble would be about the gong. A gong is a class of percussion instruments. The specific type that is common in orchestras is called a tam-tam, and that is typically how it is referred to in scores. I think "gong" would be acceptable is a type-in, but I'd prefer to see the tam-tam as the correct answer in the quiz.