a. possible but not necessary; left to personal choice
常见例句
1
the optional second part of a PC computer filename n the most direct or specific meaning of a word or expression
2
(in fact, even remembering your best friends birthday is optional)\r \r
3
in an optional manner
4
dress was optional but intended to shock (plastic garbage bags or old school uniforms) and hair was dyed in bright colors (in Mohican haircuts or sometimes spiked in bright plumes) n
