在室温条件下,下列措施中,哪一项不利于提高光合作用强度?( )
已知α、β∈(0,π),且tanα、tanβ是方程x2﹣5x+6=0的两根.
①求α+β的值.
②求cos(α﹣β)的值.
Which of the following signs can you often see next to a lake?