$36 \cdot 49$ 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)
［Solution］The hour hand does not overlap with the minute hand in the following time periods:
$$
2:30 \sim 3:00, 12:45 \sim 13:00, 18:00 \sim 18:30
$$
The hour hand and the minute hand will overlap once between 7:35 and 7:40. Therefore, the correct choice is $(B)$.