$36 \cdot 49$ the hour and minute hands overlap once in the following time period:
(A) $2: 30 \sim 3: 00$.
(B) $7: 30 \sim 7: 45$.
(C) $12: 45 \sim 13: 00$.
(D) $18: 00 \sim 18: 30$.
(2nd "Five Sheep Cup" Junior High School Mathematics Competition, 1990)