题目

    People are always asking what the most important element to a healthy relationship is. The    41    is there are many. But there is one really important thing that all great and healthy relationships have in common-_42  .  Yes, of course, there are some little    43 lies even in the best of relationships-44  surprises or unexpected birthday parties-but the truth is that happy couples communicate honestly and don't    45    to protect their own interests. So how can you have more open    46    in your own relationship?     First, remember that honesty 下列实例中，机械能不守恒的是(不计空气阻力)(    )A.物体做自由落体运动B.物体沿光滑固定曲面下滑C.小球落在直立的轻弹簧上，把弹簧压缩后又被弹起D.水平飞来的子弹射穿放在光滑水平面上的木块