题目内容
（请给出正确答案）
[主观题]
According to the passage, ______.A．security alarm systems can only be installed in commerc
According to the passage, ______.
A．security alarm systems can only be installed in commercial and industrial establishments and in large homes
B．security alarm systems are still very expensive
C．now, people can buy low-cost security alarm systems and install themselves
D．security alarm systems can't scare off vandals
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