All of the following are types of firewall except（）
A. Packet Filtering Firewall
B. Proxy Firewall
C. Stateful Inspection Firewall
D. IDS Firewall
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Promoting products and brands by Gmail belongs to__（）
A. online advertising marketing
B. mailing list marketing
C. IM marketing
D. Email marketing
Compared with plastic materials, the biggest characteristic of the tensile mechanical properties of brittle materials is（）
A. Low intensity
B. Small deformation under the same tension
C. There is almost no plastic deformation before fracture
D. The stress-strain relationship strictly follows Hooke’s law
The difference between O2O model and B2C model is that__（）
A. O2O model means that after consumers purchase goods and services online, they must go offline to enjoy services
B. O2O model allows consumers to pay offline
C. B2C model requires consumers to pick up the goods at the merchants
D. O2O allows merchants to have no offline physical stores
All of the following statements about digital time stamps are true except（）
A. The digital timestamp is provided by the DTS service organization
B. Time-stamped files can be modified
C. The digital time stamp is used exclusively to prove the time the message was sent
D. It is not possible to timestamp a file with a date and time different from the current date and time
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