Check these two answers? Someone gave me 60 degrees for the answer of question e, but I think that it's 90. Could someone explain this?

The diameter of circle C is 18 cm. Chord AD is the same length as a radius. Use this information, the diagram, and your experiences in geometry this semester to answer these questions. (Use pi = 3.14.)

d.) How does the length of arc AD compare to the length of arc AB? (my answer: Arc AD is half of arc AB).

e.) If EF = 1/2(BD), then what is the degree measure of arc EF? (my answer: 90 degrees).

Image of the circle: http://i.imgur.com/sloZ0jb.png

Question

Check these two answers?  Someone gave me 60 degrees for the answer of question e, but I think that it's 90. Could someone explain this?

The diameter of circle C is 18 cm. Chord AD is the same length as a radius. Use this information, the diagram, and your experiences in geometry this semester to answer these questions. (Use pi = 3.14.)

d.)	How does the length of arc AD compare to the length of arc AB? (my answer: Arc AD is half of arc AB).

e.)	If EF =  1/2(BD), then what is the degree measure of arc EF? (my answer: 90 degrees).

Image of the circle: http://i.imgur.com/sloZ0jb.png