What is the difference between hard bounces and soft bounces?

What is the difference between hard bounces and soft bounces?
A . A hard bounce happens when an email is rejected by a spam filter; a soft bounce means an email address is invalid.
B . A hard bounce renders a lead email address invalid; a soft bounce gets automatically resolved within a few days.
C . A soft bounce renders a lead email address invalid; a hard bounce gets automatically resolved within a few days.
D . A soft bounce happens when an email is rejected by a spam filter; a hard bounce means an email address is invalid.

Answer: B

Explanation:

Reference: https://docs.marketo.com/display/public/DOCS/Hard+and+Soft+Bounces+in+Email