So we need to find an answer choice that explains the least as to WHY HALF THE POPULATION DISAPPEARED AND NO RISE IN WAGES OCCURRED. Please note in the premise that the reason wages were increased because the lack of workers made labor so much more expensive.

lack of workers = more expensive labor = increased wages


(A) Improved medical care reduced the mortality rate among able-bodied adults in the decade following the famine to below prefamine levels.
Medical care improved and thus less people are dying. This means that the labor force did not diminish as much as it could have been. It's a good reason why wages are still high, because the labor force is still existent.

(B) Eviction policies of the landowners in Ireland were designed to force emigration of the elderly and infirm, who could not work, and to retain a high percentage of able-bodied workers.
B was the most missed answer. It states that the elderly were evicted and thus forced to leave the country. It also states that the elderly couldn't work anyway and that Ireland retained a high percentage of their labor force. B is a sound reason as to why the population of Ireland was severely cut but why the wages did not reduce.

(C) Advances in technology increased the efficiency of industry and agriculture, and so allowed maintenance of economic output with less demand for labor.
If technology was so efficient then Ireland probably did not need workers. Thus we don't need to pay workers extra.

(D) The birth rate increased during the decade following the famine, and this compensated for much of the loss of population that was due to the famine.
Babies don't make up the labor force. Plain and simple. Even in the next decade these kids will still be too young to be part of the workforce.

(E) England, which had political control of Ireland, legislated artificially low wages to provide English-owned industry and agriculture in Ireland with cheap labor.
States that England kept wages low. Simple to rule out.