How can a browser trust a web-server certificate signed by a third party CA?

How can a browser trust a web-server certificate signed by a third party CA?
A . The browser must have the CA certificate that signed the web-server certificate installed.
B . The browser must have the web-server certificate installed.
C . The browser must have the private key of CA certificate that signed the web-browser certificate installed.
D . The browser must have the public key of the web-server certificate installed.

Answer: A