应用题必须用蓝、黑色钢笔或者圆珠笔写在答题纸的相应位置上,否则无效。请根据图5所示网络结构回答下列问题。
查看答案
In the 16th and 17th centuries, two persons helped lay the foundation of modern education
A—piano B—violin
C—cello D—guitar
E—xylophone F—harp
G—oboe H—clarinet
I—drum J—gong
K—cymbals L—dulcimer
M—viola N—flute
O—Erhu P—accordion
Q—suona horn
51. ()大提琴 ()小提琴
52. ()笛 ()鼓
53. ()钢琴 ()中音提琴
54. ()吉他 ()锣
55. ()手风琴 ()唢呐
网络防火墙的主要类型为包过滤路由哭、应用级网关和_____网关。