常见的酸均溶于水，而原硅酸（H4SiO4）不溶于水，其中硅元素的化合价是 [ ]
A．+1
B．+2
C．+3
D．+4
答案：D
The first edition of the magazine was published in 1960, and has been a best-seller _______. [ ]
A. ever since
B. till then
C. ever before
D. after that
巡检及维护项目质量控制点包括哪些（）
A.巡检计划审核
B.维护项目验收
C.巡检工作质量检查
D.维护项目方案审核
