In speech, it is fine to use "because' at the beginning of a sentence. However, some people say it is not considered good style to do this in writing. I wonder if it is correct to use "It is" before "because" while answering the following sentence. Please note that the following question is in present tense.
Question: Why do the pirates need to keep their ship light?
Answer: It is because it let the ship move fast.
Many thanks for your help!