0.23×2－0.46＝____
⑴Here you are.____ A. Yes, I do.
⑵Is this your watch?____ B. It's a watch.
⑶What's it?____ C. Thank you.
⑷Do you like apples?____ D. No,it isn't.
绍兴市应征入伍赴藏的青年，刚到达青藏高原时，常会头晕、头痛、耳鸣，有的甚至恶心、呕吐，其主要原因是( )
