2015年4月28日召开国务院常务会议确定，加快清洁油品生产供应，力争提前完成成品油质量升级任务．清洁汽油添加剂异辛烷（C₈H₁₈），能改善油品质量，促进汽油燃烧，大幅减少车辆污染物排放，有效保护大气环境．请回答：

（1）异辛烷中碳氢两原子个数比为____ ；

（2）异辛烷的相对分子质量为　____ ．

阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。

     Joe is interested in getting exercise and competing (竞争) on a team. He reads about the events at the local pools and finds the perfect activity.

                                                                           Swimming Programs

     Summer Swim Team

     Join a Summer Swim Team and compete with other swimmers! The program is offered at eight different local pools for youths to 17 years old. The season runs June 21-August 21. Practices are daily (Monday through Friday) throughout the summer. Cost: $50.00.

     Junior Swim Instructor (少年游泳教练)

     Two weeks, 20 hours of instruction, two hours per day for children 11-14 years old. Pre-training for youths interested in becoming swim instructors ($45 per child).

     Junior Lifeguard (救生员)

     Two weeks, 30 hours of instruction, three hours per day for children 11-14 years old. Pre-training in lifeguarding, and customer (消费者) service ($45 per child).

     Junior Swim Instructor & Junior Lifeguard Training Dates

     Special Offer

     Anyone who takes part in both junior swim instructor and junior lifeguard programs at the same time need only spend $75 instead of $90 for 50 hours of training.

     Register(注册) Online

     You can now register online! Visit our website at http://www.example.com. You can choose an area of town, a specific local center, a program, or search for classes which can meet the needs of students of different ages. Just visit our website, and you're on your way!

填空

友字共有____笔，第三笔是____。

已知函数$f\left(x\right)=\ln (x+\sqrt{x^2+1})$，若实数$a,b$满足$f\left(a\right)+f(b-2)=0$，则$a+b=$ (　 )