无釉面陶瓷地砖颜色有多种，形状为正方形，也有矩形或异形。厚度为（），砖背面一般有凹槽，利于与基层粘贴牢固。

A.5～10mm

B.10～15mm

C.15～20mm

D.10～20mm

Besides the electrons, an atom also contains positive electrical particles()total charge must be equal to that of the electrons.

A. which

B. that

C. whose

D. of which