下列说法中不正确的是[ ]
A.互为相反数的两数的和为零
B.在数轴上,互为相反数的两数到原点的距离相等
C.零没有相反数
D.只有正负号不同的两个数互为相反数
答案:C
When and why he came here ________ yet.
A.is not known
B.are not known
C.has not known
D.have not bee
为什么在常温下,大多数无机非金属材料不具备明显的塑性?