Don't____(担心) about your grandpa. Take some medicine, and he'll be better soon. Thank you, Doctor Li.
把下列词语补充完整。
叽叽____ 又跳 ____
—________
已知|a→|=2|b→|≠0,且b→⊥(a→﹣b→),则a→与b→的夹角是( )