What we have here is a congenital intolerance to breast milk: galactosemia, in which the body cannot convert galactose to glucose (resulting in an accumulation of Galactose 1-phosphate). They then list the findings and tests used to diagnose it. Lactose (the disaccharide in milk) is composed of glucose+galactose.

If you didn't understand the tests in the stem, this should help:

Urine reducing substance test: https://study.com/academy/lesson/reducing-vs-non-reducing-sugars-definition-comparison.html

Glucose oxidase test: catalyzes the oxidation of glucose to hydrogen and D-glucono-delta-lactone. If there is no glucose present (i.e. with galactosemia), the test will be negative because there is nothing for the test to catalyze.

UWORLD 1067: Fructose, glucose, and galactose are reducing sugars and can be detected by a copper reduction test, which nonspecifically detects the presence of reducing sugar. A urine dipstick, uses glucose oxidase to ascertain the presence of urinary glucose and will not test positive in the presence of fructose or galactose.