Please help so I can pass

Fractions can be added and subtracted only if they're fractions. a. like b. proper c. improper d. unlike

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Acylinder with a base diameter of x units has a volume of jxcubic units which statements about the cylinder are true? check all that apply. the radius of the cylinder is 2 x units. the radius of the cylinder is 2x units. the area of the cylinder's base is 200 square units. the area of the cylinder's base is a square units. the height of the cylinder is 2x units. the height of the cylinder is 4x units. mark this and return save and exit next submit