选择填空。

— What time is it?

— It's ______. [ ]

A. four four-five

B. a quarter to five

C. forty-five four

与烤瓷冠桥不透明层有气泡无关的因素是

A．烤瓷合金多次重复使用

B．基底冠老面多方向打磨

C．使用不正确的金刚砂车针打磨基底冠

D．铸道安插不正确

E．遮色瓷层过薄