# The equation DU = Tds – PdV is applicable to infinitesimal changes occuring in_________________?

**The equation DU = Tds – PdV is applicable to infinitesimal changes occuring in_________________?**

A. An open system of constant composition

B. A closed system of constant composition

C. An open system with changes in composition

**D. A closed system with changes in composition**** (Correct)**