This core has stayed hot over the billions of years since. Every kilometer you go down, it gets about 25 degrees Celsius hotter (or 1 degree Fahrenheit per 70 feet). The core will never freez
over. Scientists estimate it would take about 91 billion years for the core to completely solidify. The sun will burn out long before that time!
Which two words would BEST replace estimate" and "solidity in the paragraph above?
(A) guess; freeze
(B) hope; set
(C) predict: harden
(D) assume, congeal