The correct answer is C. They look
Step-by-step explanation
Sentences are made up of several elements that are subject, verb and predicate, in addition, theymust have coherence and cohesion so that the message you want to transmit is well understood by the receiver. According to the above, the sentence "I can see that you have just dyed your hair chestnut. They look very beautiful now" has an error because in the first part "I can see that you have just dyed your hair chestnut" refers to "her hair" as the object of the sentence and in the second part of the sentence refers to it as "they", then it would not have cohesion and it would be a mistake. According to the above, the correct answer is C. They look.