WARNING boring technical post!
This instrument course can be frustrating! Leave it to the FAA to make the simplest straightforward concept confusing and ask a question in a way to make you answer incorrectly even through you can quote FAR 91.211.
Given the IFR Low chart excerpt in Fig 89, since there is no MCA, you could cross BCE at 11,600-12,000 and then start your climb to the MEA. Therefore I could cross BCE at 11,600 and begin a climb to 16,000. As per 91.211 required crew would not have to use oxygen until 12,501 ft has been exceeded for 30 min and the passengers oxygen available above 15,000.
Given the 91.211 no answers are totally correct but B is best. NOPE. The “correct” answer is C. Evidently they are assuming you cross BCE at the MEA.
Question 6 is phrased correctly.
Believe me you have to look carefully at exactly how the question is worded otherwise if I were to assume as they do in question 5 I would get many wrong answers.