2. 选择题.
(1)如图,$AB是\odot O$的直径,点$C在\odot O$上,若$\angle A = 40^{\circ}$,则$\angle B$的度数为()

A. $80^{\circ}$ B. $60^{\circ}$ C. $50^{\circ}$ D. $40^{\circ}$
(2)如图,把直角三角板的直角顶点$O$放在破损的玻璃镜的圆周上,两直角边与圆弧分别交于点$M$,$N$,量得$OM = 8$ $cm$,$ON = 6$ $cm$,则该圆玻璃镜的半径是()

A. $\sqrt{10}$ $cm$ B. $5$ $cm$ C. $6$ $cm$ D. $10$ $cm$
(3)如图,$\triangle ABC内接于\odot O$,$OD\perp BC于点D$,$\angle A = 50^{\circ}$,则$\angle OCD$的度数是()

A. $40^{\circ}$ B. $45^{\circ}$ C. $50^{\circ}$ D. $60^{\circ}$
(4)如图,在$\odot O$中,$\angle CBO = 45^{\circ}$,$\angle CAO = 15^{\circ}$,则$\angle AOB$的度数是()

A. $75^{\circ}$ B. $60^{\circ}$ C. $45^{\circ}$ D. $30^{\circ}$
(5)如图,已知$BD是\odot O$的直径,点$A$,$C在\odot O$上,$\overset{\frown}{AB}= \overset{\frown}{BC}$,$\angle AOB = 60^{\circ}$,则$\angle BDC$的度数是()

A. $20^{\circ}$ B. $25^{\circ}$ C. $30^{\circ}$ D. $40^{\circ}$
(6)如图,已知$AC是\odot O$的直径,点$B$在圆周上(不与点$A$,$C$重合),点$D在AC$的延长线上,连接$BD交\odot O于点E$,若$\angle AOB = 3\angle ADB$,则下列选项中正确的是()

2.
(1)C
(2)B
(3)A
(4)B
(5)C
(6)D