【单选题】The thick smog covered the whole city. It was as if a great black blanket ______ over it.
【单选题】The thick smog covered the whole city.It was even if a great black blanket that had been thrown over it.
【单选题】The thick smoke covered the whole city. It was _____ a great black blanket had been thrown over it.
【单选题】并行数据通信时指以( )为单位的数据传输方式。