anand--
You lost me there. Are you saying that I should explain myself? Or that I should change my answer? Or that I provided the correct answer to a stupid question?
a. The use of carrier pigeons is usually preferable to the use of portable
electronic devices when a military unit needs a way to send classified
military information.
There's no reason to believe that this is true in the strong form in which it is stated.
From the argument:
use of portable electronic devices whose signals can be intercepted.
It's a little nuanced, but the argument does not state:
use of portable electronic devices, whose signals can be intercepted.
In other words, the argument does not claim that all portable electronic device signals can be intercepted. It states that
some can be intercepted.
And it sates that pigeons can be "valuable". Not that they're preferable.
b. The messages that carrier pigeons carry cannot be intercepted.
Too strong of an inference, though not a terribly bad choice, IMO.
c. The use of carrier pigeons decreased once portable electronic devices
became practical in warfare.
We know that pigeons showed up in the earliest records. We know that they were used "extensively" in WWI and WWII. Today, they're merely "valuable" as an alternative. That seems like declining use to me.
d. Carrier pigeons were used in warfare prior to the date of the earliest
known record of wartime activity.
The argument did not state this! No reason to assume this. They were used at the date of first record, but it could be (for example) that only when literacy began to become widely held that people recorded of wars, and that you can only send written messages if you know how to write...
e. Carrier pigeons are still used extensively by modern military units.
We all know that this is wrong.