=-(x？ -5x+4)

=-(x-5x+6.25)+2.25

=-(x-2.5)？ +2.25

≤2.25

That is A={y|y≤2.25}

In other words, a stands for all real numbers less than or equal to 2.25.

So 1∈A, 4 doesn't belong to A, so choose B.

(1) 1, 4 is two random numbers, the difference is 1

(2) A = {...}, indicating what set A specifically refers to.

(3)A is not Y in the set, and Y is an element in A..