Question

they test the balloons before the parade? *
by weighing them
by filling them with air
by measuring their size
by painting them

Explanation:

To test balloons before a parade (likely for floatability, like in Macy's parade), weighing them checks if the balloon (with helium, typically) has the right lift. Filling with air doesn't test buoyancy for flight. Measuring size or painting isn't a functional test for parade readiness. So "By weighing them" is the logical choice.

Answer:

A. By weighing them