Which one of the following statements about the GTPase-activating protein (GAP) and the guanine exchange factor (GEF) that modify Ran is true?
A. Cytosolic Ran GEF promotes formation of Ran-GDP in the cytosol.
B. Nuclear Ran GEF promotes formation of Ran-GTP in the nucleus.
C. Nuclear Ran GAP promotes formation of Ran-GDP in the nucleus.
D. Cytosolic Ran GAP promotes formation of Ran-GTP in the cytosol.