2014. The line graph shows the average proton speed, in kilometers per second (km/s), measured in the solar wind by Earth-orbiting satellites at the start of each hour over a period of time beginning on May 20, 350 340 330 Average proton speed (km/s) 320 310+ 2:00 a.m. 4:00 a.m. 6:00 a.m. 8:00 a.m. 10:00 a.m. 12:00 p.m. 2:00 p.m. Time 4:00 p.m. 6:00 p.m. 8:00 p.m. 10:00 p.m. 12:00 a.m. 2:00 a.m. According to the line graph, what was the average proton speed, in km/s, at 4:00 a.m.? A) 345 B) 338 C) 330 D) 314