"unable is preferred to "can not" because it specifies the lack of ability inherent in the animal. Because the moose is orphaned he does not have the ability to protect itself. Cannot is much less specific and could refer to a barrier outside the animal such as "the moose cannot cross the river because the water is too deep".

"disadvantaged" is generally used to refer to people and includes such things as lack of resources or education.

Likely and liable are often used interchangeably except that "liable" implies a negative outcome whereas "likely" can also be positive.

A.
Here is how I arrived at the answer: First I eliminated liable choices as it gives a sense of certainty. I am "Liable to pay" vs likely which may or may not happen. Choice B is awkward..."likely severely disadvantaged". So we are left with A & E. Again for E "often likely to be unable that it can" kind of awkward.

Hope this helps as I used elimination method to arrive at the answer.

Disagree about liable. It does not imply certainty. From the online dictionary:

Liable is often interchangeable with likely in constructions with a following infinitive where the sense is that of probability: The Sox are liable (or likely ) to sweep the Series. Some usage guides, however, say that liable can be used only in contexts in which the outcome is undesirable: The picnic is liable to be spoiled by rain. This use occurs often in formal writing but not to the exclusion of use in contexts in which the outcome is desirable: The drop in unemployment is liable to stimulate the economy. Apt may also be used in place of liable or likely in all the foregoing examples. See also apt, likely.

Actually, in answer to your question which you resent me Shimbal80, Tani Wolff answered it nicely and I agree with the rest of her points.

I might add that 'unable' is more concise than 'cannot'. They are synonymous- although maybe there is a nuanced difference in that 'unable' further specifies the non ability to do something whereas 'cannot' does not specify ability/non ability (some can read it as implied and this may be true sometimes), so in this case I would even say that 'unable' is better because of its conciseness and its specificity of meaning, although they are essentially the same.

In addition, to be at a severe disadvantage is a perfectly fine expression.

Finally, see Tani Wolff's comments on the rest of the points especially liable/likely and disadvantaged/at a disadvantage.

Tani Wolff - Kaplan wrote:"unable is preferred to "can not" because it specifies the lack of ability inherent in the animal. Because the moose is orphaned he does not have the ability to protect itself. Cannot is much less specific and could refer to a barrier outside the animal such as "the moose cannot cross the river because the water is too deep".

"disadvantaged" is generally used to refer to people and includes such things as lack of resources or education.

Likely and liable are often used interchangeably except that "liable" implies a negative outcome whereas "likely" can also be positive.

can you please explain me what wrong with B?