Which choice completes the text so that it conforms to the conventions of Standard English? In 1453, English King Henry VI became unfit to rule after falling gravely ill. As a result, Parliament appointed Richard, Third Duke of York, who had a strong claim to the English throne, to rule as Lord Protector. Upon recovering two years later, ______blank forcing an angered Richard from the royal court and precipitating a series of battles later known as the Wars of the Roses.

Choice A is the best answer. The convention being tested is subject-modifier placement. This choice ensures that the introductory phrase 'upon recovering two years later' appears immediately before the noun it modifies ('Henry'), clearly establishing that Henry recovered two years later. Choice B is incorrect because it results in a dangling modifier. The placement of the noun phrase 'the reign of Henry' immediately after the introductory phrase illogically suggests that the reign of Henry recovered two years later. Choice C is incorrect because it results in a dangling modifier. The placement of the noun phrase 'Henry's reign' immediately after the introductory phrase illogically suggests that Henry's reign recovered two years later. Choice D is incorrect because it results in a dangling modifier. The placement of the function word 'it' immediately after the introductory phrase illogically suggests that 'it' recovered two years later.