There is free firewall software available that can run on minimal hardware and provide a good level of (71) to your network.

A．protective

B．profectiog

C．protection

D．profection

标准群钻，它是在普通麻花钻的钻尖上，磨出两个对称的月牙形圆弧槽，修磨减窄（），形成两条较锋利的内刃。对于直径较大的钻头，还在一侧外刃上两出1～2条分屑槽。

A.主切削刃

B.横刃

C.棱边

D.立刃