7. 1 ~ 7.2 Reference answers for level test 1, 1. C 2。 B 3。 D 4。 D 5。 C 6。 A seven. D 8。 C 2，9.80 10.50 1 1.20 12。 Stable 13. Right triangle14.18,54, 108 15.2 (2) It is the most economical to choose a wooden stick with a specification of 3m. 19. Because ∠ADE is the outer corner of △BDF, ∠ ade = ∠1+∠ b = 87+28 =165438. So ∠ e =180-∠ a-∞△ BDF =180-30-15 = 35. Four, twenty. (1 (2)AD is the height of △ABC, △ABD and △ACD; (3)BF is the center line of △ABD. 2 1. Because AE divides ∠BAC equally, ∠ BAE =12 ∠ BAC =12× 80 = 40. Because ad BC, ∞. Because ∠ bad+∠ b+∠ ADB = 180, ∠ bad =180-∠ b-∠ ADB =180-60-.