A piece of plastic (sample Q), was heated at a constant rate. After 20 minutes of adding heat, the plastic melted. When an identical piece of plastic (sample R), was heated with twice as much heat per minute, the plastic melted in 10 minutes. How do the melting points of the two pieces of plastic compare? A. The melting point of sample R is double that of sample Q. B. The melting points of sample Q and sample R are the same. C. The melting point of sample R is slightly higher than sample Q's. D. The melting point of sample Q is higher than sample R's.