Official Answer:-

Read the sentence, looking for clues

A stand of trees is estimated to be 10,000 years old, one of the oldest living things.

Predict an answer

Since the blank describes the trees, and all that's known about them is that they're very old, a good prediction would be "ancient".

Select the choice that most closely matches your prediction

(B) primeval means “primitive” or “ancient,” making this the correct answer. The sentence provides no indication that the organism is(A)desiccated, which means "dehydrated" or "dried out" but implies nothing about the trees' ages. (C) cultivated suggests that the trees have been cared for by people, which, since the trees have been growing “on a remote Tasmanian mountain” for 10,000 years, is highly unlikely. (D)sizable is incorrect because there's no indication of how big this particular stand of trees is. (E) moribund, or "near death" is unsupported by the sentence's context; the trees may be particularly old, but there's no reason to think they're at the end of their lifespan.

Check your answer

A primeval stand of densely interconnected Huon pine trees on a remote Tasmanian mountain has been estimated by biologists to be up to 10,000 years old, placing it among the oldest living organisms on the planet.

TAKEAWAY: Be careful of words that seem to fit the general context of the sentence but which have no specific support.