Simplify the following text for a Grade 5 native English-speaking person.
Original: In the 19th and 20th centuries , organ builders began to build instruments in concert halls and other large secular venues , allowing the organ to be used as part of an orchestra , as in Saint-Sa Ã `` ns ' Symphony No. 3 .
Simplified: There is an important organ solo in Symphony no 3 by Saint-Sa Ã `` ns .