Misc: When they mate, a yak and a cow produce a?

Questions

Tchaikowsky's "Marche Slave" is based on a folk-song of what national origin ?

Which pianist-composer permanently injured his hand by wearing a home-made contraption designed to immobilize the fourth finger while practising ?

French writer George Sand is remembered for her affair with which composer ?

Bach's "Goldberg Variations" are best known today through the recording of this Canadian pianist. ?

What composition was structured on a single theme repeated over and over ?