[单选题]
A gas is allowed to expand *m4 shk6p z5esawz(g ,0ziz:ustrg9e6l. 1uwat constant2 kys(w,z9hh5j)zr w; sbxunihvr s2/cx* :4f pressure as heat is added to it. This process5sz2k42xys) rf iv *zchhwj(:/u x,9 nwbrh s; is
A. isothermal
B. isochoric
C. isobaric
D. adiabatic
