I'm Peter. There are four people in my family. They are my father, my mother, my grandfather and me. I'm twelve. My birthday is on 15th March. My parents are both doctors. They help people. Their birthdays are both in May. My grandfather is old. He is sixty-five. His birthday is on 9th June. He likes reading. I like reading too. I want to be a teacher in the future. I want to teach Chinese in a school.

shirt和fish中的“sh”字母组合发音相同。

如图所示，甲、乙、丙三个轮子依靠摩擦传动，相互之间不打滑，其半径分别为r₁、r₂、r₃．若甲轮的角速度为ω₁，则丙轮的角速度为（   ）

设$\overrightarrow{a}$、$\overrightarrow{b}$是不共线的两个向量，已知$\overrightarrow{AB}$=2$\overrightarrow{a}$+k$\overrightarrow{b}$，$\overrightarrow{CB}$=$\overrightarrow{a}$+3$\overrightarrow{b}$，$\overrightarrow{CD}$=2$\overrightarrow{a}$﹣$\overrightarrow{b}$，若A、B、D三点共线，求k的值．