Able Mailed Conover an Offer That Stated in Part, "You

Able mailed Conover an offer that stated in part, "You must accept by sending me a certified letter which must be received by me on or before February 1^st." Conover may accept by

A) sending a telegram of acceptance to reach Able by February 1^st.
B) making a phone call to Able on February 1^st.
C) mailing his acceptance on February 1^st.
D) sending Able a certified letter mailed in time to reach Able by February 1^st.