[单选题]
What is the primary factor keeping women fr l yr/g6y/-tngsk j,4 jb20vduom 5 hs rrsy11*wu8yqg)w taking top leadership positions according to theu1whg*yr1 rqy s) 8sw5 recent survey?
A. Personality traits.
B. Family responsibilities.
C. Gender bias.
D. Lack of vacancies.