Atrain approaches a railroad crossing, blowing its whistle the entire time. when does an observer at the crossing hear the lowest frequency of the train’s whistle?

The observer will hear the lowest frequency of the whistle as the train passes. As the train approaches, the whistle will appear to increase in pitch as it approaches. When it passes, the sound will decrease in pitch as it moves further away. The effect observed here is the Doppler Effect.  It occurs when there is motion between the source of the sound and an observer or receiver. 

Julia would be observing a. static electricity was caused by her sweater rubbing against her shirt and transferring electrons. she didn't touch anything metal, so that would cancel out b.she most likely didn't rub her sweater against her hair either, so that cancels out c.she also didn't scoot across the carpet while trying to take her sweater off, that cancels out d.so that leaves a.a. is correct.