根据所给要求，改写下列句子。每空格限填一词

67. At last Tom let his brother go to the concert instead of himself. (改为否定句)

   At last Tom __________ __________ his brother go to the concert instead of himself.

68. Daniel was keen on playing tennis when he was ten years old. (保持句意基本不变)

Daniel was __________ __________ playing tennis when he was ten years old.

69. A lot of young students go to America because they want to further their study. (就划线部分提问)

   __________ __________ a lot of young students go to America?

70. It was very cold yesterday. He couldn’t go swimming. (合并为一句)

   It was __________ cold for him __________ go swimming yesterday.

71. We must keep our classroom clean and tidy every day. (改为被动语态)

   Our classroom must __________ __________ clean and tidy every day.

72. The farmers stopped working in the fields when the sun set. (保持句意基本不变)

   The farmers __________ stop working in the fields __________ the sun set.

73. “Will they come to attend the meeting?” asked the boss. (改为宾语从句)

The boss asked __________ they __________ come to the meeting.