Consider the following statements regarding the challenges faced by historians when using manuscripts as sources:

a. Scribes never introduced errors or changes when copying manuscripts by hand.
b. The original manuscript of an author is often available to researchers, making their work easier.
c. Differences in manuscript versions are a serious challenge as they could become substantially different over centuries of copying.
d. Historians have to compare different manuscript versions of the same text to deduce what the author originally wrote.

Choose the correct option from below: