Chang, an NRA, Is Employed by Fisher, Inc

Chang, an NRA, is employed by Fisher, Inc., a foreign corporation. In November, Chang spends 10 days in the United States performing consulting services for Fisher's U.S. branch. She earns $5,000 per month. A month includes 20 workdays.

A) Chang has $2,500 U.S.-source income which is exempt from U.S. taxation, because she is in the U.S. for 90 days or less.
B) Chang has $2,500 U.S.-source income which is exempt from U.S. taxation, because the amount paid to her is less than $3,000.
C) Chang has $2,500 U.S.-source income, because her foreign employer has a U.S. branch.
D) Chang has no U.S.-source income, under the commercial traveler exception.