A cross over at the front of the stroke tends to cause your elbow to drop, also damaging your catch and hurting your propulsion.
身前的划水过中线易于使你的肘部下沉，而且破坏你的抓水和损害你的动力。
In front and on either side of them were the control panels for LM's guidance, communications, environment, and propulsion systems.
在他们面前和两边，是登月部分的响导通讯、环绕和推进系统。
The front roll (active roll)realizes automatic track-propulsion;
前辊（活动辊）实现自动跟踪推进；
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