Which statement about horizontal stretch and reflection is true

Well I'm not exactly sure what you mean I can describe how horizontal stretching, compression, and reflection.

so in quadratic equations in vertex or quadratic form

and just to clear the air (^2) means to square or have an exponent of 2

Quadratic Form: ax^2 + bx + c

Vertex Form: a (x-h)^2 + k

In both of these equations the a controls the reflection, compression, and stretch of the graph over the vertex.

so if the variable a is. . .

between 0 and 1: it will compress by that number. . .so if a = 1/2 then the graph is compressed by 1/2

number larger than 1: it will stretch by that number. . .in turn if a = 2 then the graph is stretched by 2

lastly reflection is determined by if a is positive or negative. If a is negative than it reflected going downward (or negatively) rather than upward (positively).