已知向量$\overrightarrow{m}$=（cosA，﹣sinA），$\overrightarrow{n}$=（cosB，sinB），$\overrightarrow{m}$•$\overrightarrow{n}$=cos2C，其中A、B、C为△ABC的内角．

求角C的大小；

分析下列材料，回答相关问题．

材料一  据报道，截至2013年4月26日，我国已确诊H7N9禽流感病例112例，死亡23例．H7N9禽流感是由H7N9病毒引起的一种急性呼吸道传染病，该病毒主要通过人与带病禽畜接触传播，目前尚未发现人传人的现象.

材料二  自我国发生人感染H7N9禽流感以来，出现了扎堆注射流感疫苗的现象，但医生说，由于流感疫苗是根据上一年度病毒毒株研制的，因此对今年新型病毒或病毒变种的预防效果有限，专门针对H7N9的疫苗尚未生产出来．

⑴Why can't you eat the cake?____            A. You can walk there.

⑵How do I get to the bus stop?____         B. No, he can't. He's too young.

⑶Where's the soup?____                           C. No, it's in June.

⑷What's wrong with Tom?____                 D. They are playing football.

⑸What are the boys doing?____               E. It's in May.

⑹Can Bobby ride a bike?____                   F. It smells nice.

⑺How's the meat?   ____                          G. Because it's too sweet.

⑻Does Lily like singing?____                    H. His arm hurts.

⑼When's Mother's Day?  ____                  I. It's on the table.

⑽Is your birthday in May?  ____               J. Yes. She sings well.