Answer:
D, but careful on conventions
Step-by-step explanation:
Honestly, it's a matter of conventions. Either C or D, then it's a matter on what whoever wrote the book likes and how he got taught. For example, for me, [tex]log_{10} x = Log x =[/tex], please note the capital L, and [tex]log_e x = ln x[/tex], in order to avoid any confusion - if someone has a terrible handwriting and their capital and small Ls look too similar.