Which statement is true about a Smurf attack？（）
A. It sends ping requests in segments of an invalid size
B. It intercepts the third step in a TCP three-way handshake to hijack a session
C. It sends ping requests to a subnet， requesting that devices on that subnet send ping replies to a targetsystem
D. It uses Trojan horse applications to create a distributed collection of "zombie" computers， which can beused to launch a coordinated DDoS attack
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