Before Mr Larsson received his implantable device, patients had received pacing from huge external devices. 在拉森之前的很多病人通过巨大的外部设备调节心律。
A mouse is essentially a pointing device that allows the user to do many operations more quickly than he could with the keyboard alone. 鼠标是一个必要的外部设备，它可以使用户以比仅使用键盘快得多的速度完成许多操作。
