### Chinese: 它们强度很低，球打到拍子上面，振动非常大，硬球顶不住，高手都很难驾驭。
### English: They usually have low strength, leading to large vibrations when tennis balls hit on them; it is even difficult for masters to control it.
### Errors: There is no error in the English translation.

### Improved English: They are low in strength, and there will be too much vibration when the ball hits on it; it cannot withstand hard balls, and even professional cannot handle it.
