A:manageable
B:controllable
C:tolerable
D:perceivable
— Do you like black?
— No, I like it .
(x,y)
(n,n)
(m,n)
(n,m)
f(x,y)
n
m-n
m+n
则f(3,5)=____,使不等式f(2x,x)≤4成立的x的集合是____.
— I find it difficult to learn Physics well.
— That's true. Nobody can learn it well _______ he works hard at it.