男性，20岁，持续发热8d，伴食欲差，腹胀，便秘。体检：表情淡漠，心率76次/分，腹软、肝肋下1cm，脾肋下3cm，白细胞正常，嗜酸性细胞为零，血培养有伤寒杆菌生长。传染病的首要处理是

A．脱水剂应用
B．纠正水代谢紊乱
C．镇静止痉药
D．呼吸兴奋剂
E．抗病原治疗

— Tom. Why do you look so tired?

— Because I often study late ______ 10 o'clock at night.

 [      ]

A. before

B. by

C. until

D. at