Polylysine and polyglutamate are two examples of synthetic polypeptides that can assume an α‑helical structure under appropriate conditions. Identify which two synthetic polypeptides can form an α‑helix at the indicated pH values.

a. Polylysine at pH 13
b. Polyglutamate at pH 7
c. Polyglutamate at pH 2
d. Polylysine at pH 2
e. Polylysine at pH 7
f. Polyglutamate at pH 13