50 Which of the following statements can be inferred from this passage? (A) The Qinghai-Tibet Railroad is a record holder in terms of the total length of its track. (B) The completion of the Qinghai-Tibet Railroad is likely to enhance Tibet's tourism industry. (C) Thousands of engineers died of altitude sickness while building the Qinghai-Tibet Railroad. (D) The permafrost under the Qinghai-Tibet Railroad makes it necessary to breathe bottled oxygen.