Answer :

 Well, one way a solid can turn into a liquid is by melting...
Lets say we have an ice cube... An ice cube, is a solid. And if that melts, what happens? Well,  It turns into a liquid...
 How does it melt, you may ask... Well, if you apply heat to the ice, then it turns into water, in which its a liquid.
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The only way a solid can turn into a liquid is by melting. When you get a solid hot, the molecules bump around faster and harder until they start breaking apart and moving around each other; that's when a solid melts and becomes a liquid.
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