Which condition must be met in order for a web browser to trust a web server certificate signed by a third-party CA?

Which condition must be met in order for a web browser to trust a web server certificate signed by a third-party CA?
A . The private key of the CA certificate that is signed the browser certificate must be installed on the browser.
B . The CA certificate that signed the web server certificate must be installed on the browser.
C . The public key of the web server certificate must be installed on the web browser.
D . The web-server certificate must be installed on the browser.

Answer: B