But the first time we left Mat in the house unattended , he chewed up one set , and Ginger finished the other set off by crawling through them and breaking them . We ' ve replaced one , but in order to avoid the new blinds from meeting the same fate as the old ones , they are permanently tied off at the halfway mark . Which means the bottom half of our 6 ft long windows are completely exposed .

Available options:
[a]. None of the above choices ..
[b]. They wanted to have the bottom half of their windows exposed ..
[c]. Because their pets destroyed the blinds they had so that was the best solution they could come up with ..
[d]. Because they wanted to replace them ..
Q: Why did the writer tie off their blinds at the halfway mark ?
[c].