As shown in the figure, in circle O, AB is the diameter, CD is the chord, AB perpendicular  CD, the foot of perpendicular is the point E. Connect CO and AD, if angle BOC = 30.0, then the degree of angle BAD is ()
Choices:
A:30°
B:25°
C:20°
D:15°
Please directly answer the question and provide the correct option letter, e.g., A, B, C, D.
Question: As shown in the figure, in circle O, AB is the diameter, CD is the chord, AB perpendicular  CD, the foot of perpendicular is the point E. Connect CO and AD, if angle BOC = 30.0, then the degree of angle BAD is ()
Choices:
A:30°
B:25°
C:20°
D:15°
Please first conduct reasoning, and then answer the question and provide the correct option letter, e.g., A, B, C, D, at the end.
Question: As shown in the figure, in circle O, AB is the diameter, CD is the chord, AB perpendicular  CD, the foot of perpendicular is the point E. Connect CO and AD, if angle BOC = 30.0, then the degree of angle BAD is ()
Choices:
A:30°
B:25°
C:20°
D:15°