And in the mld-17th century it was common practice for ...
单项选择题And in the mld-17th century it was common practice for mathematicians to keep their discoveries and proofs secret, by writing them in cipher, code, obscure languages, or in private messages deposited in a sealed box with the Royal Society.
A.
foreign language
B.
ancient message
C.
mathematic message
D.
secret language
