Form 2555, Line # 5 Foreign Affiliate

I'm a US citizen living and working abroad. My employer is locally registered company but it has its HQ in the US. I need help with form 2555, Line # 5: 

5 Employer is (check any that apply):

a A foreign entity

b A U.S. company

c Self

d A foreign affiliate of a U.S. company

e Other (specify)

Should I select option a only? Or option a and d? What is a foreign affiliate of a US company? How do I know that my local employer is a foreign affiliate?