石油中含碳量一般在（），含氢量一般在10％―14％。 78％—88％。 80％—88％。 82％—90％。 80％—90％。
简述秘书的智力结构。
Riboswitch核糖开关
系统模型分为逻辑模型和（）。
Write a memo in about 50 words. You are a department manager. A new copying machine has been installed in your department. Write a memo to tell your staff members to be careful in using the newly-installed photocopier. Your instructions should include the following particulars: ·Ask them not to use it for too long at a time. ·Ask them to switch off the machine after use. ·Encourage them to offer suggestions for the care of the machine.
现代旅游业由哪三个部分组成？（）
