By the 16th century, Austria . . . . . . . . so large that its emperor . . . . . . . . all of modern Austria, Belgium, the Netherlands, Czechoslovakia, Hungary and Spain as well as parts of Italy and Yugoslavia.

The correct answer is: D. had become/was ruling

The 16th century was a time of great expansion for the Austrian Empire. Under the rule of Emperor Charles V, the empire grew to include

The use of the past perfect tense in the first clause (“had become”) indicates that the expansion of the empire was a completed event by the 16th century. The use of the past progressive tense in the second clause (“was ruling”) indicates that the emperor was actively ruling over this vast territory at the time.

The other options are incorrect because they do not accurately reflect the time frame or the nature of the emperor’s rule.

• Option A (“has become/ruled”) is incorrect because it uses the present perfect tense, which would indicate that the expansion of the empire is an ongoing event.
• Option B (“was becoming/has ruled”) is incorrect because it uses the past progressive tense in the first clause and the present perfect tense in the second clause. This is a non-standard use of tenses that does not make sense in the context of the question.
• Option C (“was going to become/rule”) is incorrect because it uses the future perfect in the first clause and the simple present tense in the second clause. This is also a non-standard use of tenses that does not make sense in the context of the question.
• Option E (“becomes/has been ruling”) is incorrect because it uses the present tense in both clauses. This would indicate that the emperor is still ruling over the vast territory of the Austrian Empire, which is not the case.