Which of the general advantages listed does the electrical pyrometer have over the mechanical pyrometer?（）
A. When heated, it will move proportional to the amount the metal has lengthened or expanded
B. The pointer associated with the pyrometer scale can be made to also measure engine RPM
C. It can be utilized in exhaust manifolds and heat exchangers interchangeably
D. It can indicate temperature at a distant point from the source heat
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