questions in attachments.
because an inscribed angle is equal to half its intercepted arc.
because inscribed angles that intercept the same arc are equal in measure.
because an inscribed angle in a semicircle always measures 90 degrees. It subtends 180 degrees and is equal to half of it. You don't have 90 degrees as a choice. Somebody messed up.
because arcs CD and AD make up a semicircle (180 degrees).