【简答题】REG(Resource Element Group)为( )信道资源分配的资源单位,由( )个RE组成。
【简答题】试分别说明 能量信号和功率信号的特性 。
【单选题】与牙髓炎相比,根尖周炎有其自身特点,说法错误的是:( )
【单选题】I found ___ hard to concetrate.
【单选题】After a long summer holiday in the country, I found it hard to ______ myself to the busy city life.