This says nothing about whether the parts will be difficult to obtain. We know new sirens will make the public safer. The fact that safety will only be enhanced if new sirens are installed doesn’t prove that they’ll actually be installed or that the public will actually be safer.

The author says that “if the newspaper is correct,” then the public will be safer. In other words, his conclusion only addresses the scenario in which the newspaper is correct. (B) doesn’t guarantee his conclusion because it doesn’t establish that the parts will be hard to obtain.

We can’t assume that the parts are difficult to obtain just because no other companies in the area sell them. Maybe the government could order parts online. Since it doesn’t establish that the parts are difficult to obtain, (C) doesn’t guarantee that the public will be safer.

This guarantees the conclusion that the public will be safer. Since the government can’t get parts from last year’s company, the parts will be difficult to obtain. If the parts are difficult to obtain, the government will install new sirens, which will make the public safer.

Just because the only available parts are bad quality doesn’t prove that replacement parts are difficult to obtain. The government could still buy inferior parts, which might make the public less safe. (E) doesn’t guarantee the conclusion that the public will be safer.