Mutations are important for evolution because
a. are the source of new genetic variation
b. improve the survival of organisms
c. allow individual organisms to evolve
d. remove excessive genetic variation

A. are the source of new genetic variation. And this makes sense because mutation result in new alleles and sometimes even genes. These alleles make evolution occur because it changes the structure of the gene and the phenotype. This occurred in parts of Africa and Europe in which mutations in the genes caused children of lactose intolerant parents to be lactose tolerant. 

Hope this helps :)