[单选题]
07.17: A toy car moves along x8g5vgz ,d;vx2ah7k;;b nqyi the x-axis according to the veloenrh9 m6eke;4 city versus time curve shown to the right. When does the car e; ne6khr9 4emhave zero acceleration?
A. at 2 and 4 seconds
B. at approximately 3.0 seconds
C. at approximately 3.3 and 5.1 seconds
D. the acceleration is always zero
E. at no time