51. Has knocked ( before → thì htht )
52. Iwas sleeping ( when → thì qktd )
53. Has he done / đi ( already → thì htht )
54. Was writing ( yesterday at 8 o'clock → thì qktd )
55. was translating ( when → thì qktd )
56. is working ( at the moment → thì httd )
57. has met ( for → thì htht )
58. return ( will / when → thì htđ )
59. has closed ( before → thì htht )
60 take place ( every → thì htđ )