Which of these sentences has the most formal tone?

a. We discuss herein the possibility of synergistic development strategies between our fi rm and U.S. Medical

b. Th is report explores the potential for a strategic partnership with U.S. Medical.

c. My report is the result of a formal investigation into the possibility of a strategic partnership with U.S. Medical.

d. In this report, I address the potential for a strategic partnership with U.S. Medical.