c. Why was Joseph told to name Mary's son "Jesus"?
Answer: Joseph was told to name Mary's son "Jesus" because He (Jesus) will save His people from their sins, (verse 21).
MORE INFORMATION AND/OR OTHER SCRIPTURE REFERENCES:
"Jesus" means "Savior." The literal meaning of "Jesus" is "Jehovah is salvation" or "Jehovah is the Savior." "Jesus" is the Greek form of "Joshua," which means "the Lord saves."