题目

阅读理解 Six years ago, Ann graduated(毕业)from college with a degree in Art. Now she is twenty-nine and works for a large computer company. She takes classes twice after work. She is learning to use the computer program Power Point. “I enjoy the college, but my job doesn't use the information I learned at college, ” Ann says. “The course(课程)is helping me to do my job better.” In the past, when students graduated from college and got a job, they usually stopped studying. Today lifelong learning is becoming more common. In many countries, some people return to school in their 下列函数是一次函数的是（　　）①y=-3x；②y=3x；③y=3x2；④y=3；⑤m=3n+2 A、①⑤B、①④⑤C、①④D、①②④