1头猪可以换6只羊，2只羊能换10只鸡，3头猪可换（ ）只鸡。
90
—I'm going on a trip to Japan after the exam.
－Really? _____! [ ]
A. Have a nice time
B. Congratulations
C. OK
D. It's nice of you
矿物油作为淬火介质（与水相比）的主要特点是什么？
