=>
38. C ago -> QKĐ
39. B heard/ was going to visit
40. B bị động QKHT had been V3/ed ( Before QKĐ, QKHT)
41. D by the time QKĐ, QKHT
42. B bị động QKĐ was/were V3/ed
43. D had to : phải
44. B (bị động) QKTD when QKĐ
45. B at 11:00 -> QKTD
46. B QKTD when QKĐ
47. D several times in the past -> QKHT