The expression for refractivity in terms of the Pressure and temperature coefficient is given by ____________

• A. ( frac{77.6}{T}P+4810 frac{e}{T} )
• B. ( frac{77.6}{P}T+4810 frac{e}{T} )
• C. ( frac{77.6}{P}T+4810 frac{T}{e} )
• D. ( frac{77.6}{T}P+4810 frac{T}{e} )