Written in a hurry, ___________．How can it be satisfactory?

A．they find many mistakes in the report

B．lots of mistakes have been made in the report

C．there are plenty of mistakes in the report

D．the report is full of mistakes

某移动通讯公司开设了两种通讯业务：“全球通”使用者先缴50元月租费，然后每通话1分钟，再付话费0．4元；“神舟行”不缴月租费，每通话1min付费0．6元．若一个月内通话x min，两种方式的费用分别为y₁元和y₂元．

（1）写出y₁、y₂与x之间的函数关系式；

（2）一个月内通话多少分钟，两种移动通讯费用相同；

（3）你能为用户设计一个方案，使用户合理地选择通信业务吗？

（4）某人估计一个月内通话300min，应选择哪种移动通讯合算些．