长时间不锻炼会削弱肌肉力量。

Long periods without exercise ___weaken muscle strength.

长时间的阳光直射会减弱油漆的颜色。

Prolonged sunlight ___weakens the color of the paint.

随着辩论的进行，他对自己的立场越来越不坚定了。

His confidence in his stance ___weakens as the debate progresses.