消防部队体育训练的特点：（）
A、服务专业
B、循序渐进
C、经常坚持
D、断断续续
参考答案：A, B, C
My friend has returned from the UK. She ______ at Oxford for four years, during which we communicated with each other on the Internet.
A．studied
B．has studied
C．had studied
D．has been studying
肝的主要生理功能是什么？
