Translation
My friend and I took the train from Hanoi to Nanning. It left at eight in the evening and arrived at six the next morning. We slept on the train and didn't feel tired at all when we got there.
★ 他们在火车上坐了多长时间?
Explanation
Step 1: read the question first – “多长时间” (how long) asks for a length of time, not a clock time. Step 2: find the two times in the text: the train leaves at “晚上八点” (8 p.m.) and arrives at “第二天早上六点” (6 a.m. the next day). Step 3: work it out: 8 p.m. to midnight is four hours, midnight to 6 a.m. is six more, so “十个小时” (ten hours). “八个小时” and “六个小时” are traps that simply repeat the numbers 8 and 6 from the text. The answer is B.