A:5
B:15
C:±5
D:﹣ 15
根吸收水分的部位主要是根尖的( ),这个区域生有大量的根毛.
已知sinπ+αcos-α+4πcosα=12,求cos(π2+α)值.
Susan is looking ___ the window. She is looking ___ a tree. ( )