When was drama classified as a elective?

Prairie houses a. irregular in plan, two stories high, with one-story wings b. irregular in plan, one story high, with two-story wings c. irregular in plan, two stories high , with two- story wings d. irregular in plan, one story high, with one-story wings

The energy applied to cause vibration can be in the form of air pressure a stick, bow, or electricity. true or fasle

For the difference command to work, what needs to happen?