Stuart Kovinsky wrote:Biologist: If deforestation, then K extinct
Politician: If no deforestation, then K not extinct

is the simplest way to translate the sentences.

When we say that two statements are consistent, we mean that they can both be true at the same time. Consistent doesn't mean connected.

For example:

Toronto is the capital of Ontario; and
Oranges are bumpy

are consistent statements.

When we say that two statements are inconsistent, we mean that they cannot both be true at the same time - i.e. they're contradictory.

For example:

Washington DC is the capital of the USA; and
Miama is the capital of the USA

are inconsistent statements.

So, back to our statements:

Biologist: If deforestation, then K extinct
Politician: If no deforestation, then K not extinct

We want an answer that's consistent (i.e. doesn't contradict) with the biologist and inconsistent (i.e. does contradict) with the politician.

Choice (B) gives us what we want.

"Deforestation is stopped and the koala becomes extinct"

The biologist never says that deforestation is the only problem facing the Koala; it's possible that we save the forest but all the koalas get run over by drunken Aussies in vans.

However, the politician says that stopping deforestation will definitely save the Koala. (B) clearly contradicts that statement.