______是教师教学工作的起始环节，是上好课的先决条件。
参考答案：备课
浓度为cmol/L的盐酸VmL，加水稀释到2VmL后，再从溶液中取出10mL，这10mL溶液中所含H+的物质的量是（ ）
A．0.001 mol
B．0.002cmol
C．0.005cmol
D．0.005 mol
Tom with his parents ______going to Hawaii. [ ]
A. is
B. are
C. has
D. have
