As shown in the figure, the line l parallel  m parallel  n, the vertices B and C of the triangle ABC are on the line n and line m, the angle between BC and the line n is 25.0, and angle ACB = 60.0, then the degree of angle a is ()
Choices:
A:25°
B:30°
C:35°
D:45°
Please directly answer the question and provide the correct option letter, e.g., A, B, C, D.
Question: As shown in the figure, the line l parallel  m parallel  n, the vertices B and C of the triangle ABC are on the line n and line m, the angle between BC and the line n is 25.0, and angle ACB = 60.0, then the degree of angle a is ()
Choices:
A:25°
B:30°
C:35°
D:45°
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, the line l parallel  m parallel  n, the vertices B and C of the triangle ABC are on the line n and line m, the angle between BC and the line n is 25.0, and angle ACB = 60.0, then the degree of angle a is ()
Choices:
A:25°
B:30°
C:35°
D:45°