The correct answer is: C. about
Cathrine is very careful about her long hair. This means that she is concerned about her hair and takes good care of it. She may wash it regularly, use conditioner, and style it in a way that she likes. She may also be careful not to damage her hair by using heat styling tools or harsh chemicals.
The other options are not as accurate. Option A, “in,” does not make sense in this context. Option B, “at,” could be used to describe someone who is skilled at something, but it does not make sense to say that someone is “at” their hair. Option D, “of,” could be used to describe someone who is the owner of something, but it does not make sense to say that someone is “of” their hair.
In conclusion, the correct answer is “C. about.” This is because it is the most accurate option that describes Cathrine’s relationship with her hair.