Answer choice (C) states that English kings prior to the early 17th century had much greater power relative to Parliament than the English kings of the 18th century. In other words, the political power of the kings declined from the 17th to the 18th century compared to the power of Parliament.
We can find evidence of this in the third paragraph, which states that in England "legal development [in this time] had been moving steadily toward the absolute power of Parliament." In other words, Parliament was gaining political power at the expense of the kings during this time period. The paragraph then goes on to give us examples of this shift in power: kings became subject to the law and Parliament came to be recognized as holding unlimited power.
We do not have any evidence in support of answer choice (D). This answer choice tell us that English kings prior to the 17th century developed more legal reforms than had English kings in the 18th century. Although there is evidence that kings did more in general prior to the 17th century, this answer choice specifies a particular activity: originating legal reform. We have no way to comment on how active kings were in this activity in either era.
It sounds like you correctly understood the passage, but you need to keep track of the details or new topics brought up in MBT answer choices.
I hope this helps, but let us know if you have any other questions!