Lyme disease is caused by a bacterium transmitted to people by deer ti

Understanding the argumnent -

Which of the following most logically completes the argument ?

Lyme disease is caused by a bacterium transmitted to people by deer ticks. - Fact
Deer ticks are almost never born infected with the bacterium, but they can pick it up from feeding on an infected host in any of the tick's three successive stage of development: larva, nymph, adult. - Fact
Once infected, a tick remains infected through any subsequent developmental stages, but since a tick feeds on only one host in each stage, it follows that ______________ - Facts, and we need to find an inference.

A. People can be infected only by being bitten by a tick that is either in larval stage or in the nymph stage - "only" is hyperbolic. Wrong.

B. People cannot be infected by a tick that picked up the Lyme disease bacterium in the adult stage - This can be logically deduced from the facts stated in the argument.

C. It is not possible for a person to be infected by a tick that is in the nymph stage or by a tick that was infected with the bacterium while in the nymph stage - Opposite of what is stated in the argument.

D. People infected with the Lyme disease bacterium cannot transmit bacterium to adult deer ticks - We don't know. Out of scope.

E. Only deer ticks that are adults can transmit the Lyme disease bacterium to people - Only hyperbolic, and it is the opposite of what the argument states. Ticks can transmit at any stage and not just in adults.

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­This is an inference kind of question. We need to find what we can conclude from the given premises. 

Premises:
Lyme disease is caused by a bacterium transmitted to people by deer ticks.
Deer ticks pick up bacterium from feeding on an infected host in any of the tick's three successive stage of development: larva, nymph, adult.
Once infected, a tick remains infected through any subsequent developmental stages,
a tick feeds on only one host in each stage

Conclusion: _____________________

The hint is given in what is immediately before the black: "Once infected, a tick remains infected through any subsequent developmental stages, but since a tick feeds on only one host in each stage, it follows that ______________

A. People can be infected only by being bitten by a tick that is either in larval stage or in the nymph stage

Nothing in the passage suggests that people cannot be bitten in the tick's adult stage.

B. People cannot be infected by a tick that picked up the Lyme disease bacterium in the adult stage

If it feeds on only one host per stage and if it picked up the bacterium in the adult stage from the infected host, then people will not be infected by it because it has already been fed in the adult stage (it feeds on only one host per stage). So this works. 

C. It is not possible for a person to be infected by a tick that is in the nymph stage or by a tick that was infected with the bacterium while in the nymph stage

Again no such information abotu nymph stage.

D. People infected with the Lyme disease bacterium cannot transmit bacterium to adult deer ticks

No info on whether people can infect adult deer ticks with the bacterium. 

E. Only deer ticks that are adults can transmit the Lyme disease bacterium to people

No such info given. 

Answer (B)