The answer is C. In ⅓ of cases tics resolve by adulthood, in ⅓ they become substantially less severe in adulthood, and in the remaining ⅓ they are stable. For those who experience improvement, the improvement usually begins to occur around 13 years of age but may not fully resolve until age 30.

Publication reference : Kurlan, R. Clinical Practice. Tourette’s Syndrome. NEJM. 2010. 363(24): 2332-2338.
Reference URL: https://www.ncbi.nlm.nih.gov/pubmed/21142535