The correct answer is A. HTTP.
HTTP stands for Hypertext Transfer Protocol. It is an application-layer protocol that specifies how messages are formatted and transmitted between a client and a server on the World Wide Web. HTTP is the protocol that allows web browsers to request and retrieve web pages from web servers.
DNS stands for Domain Name System. It is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participants. Most prominently, it translates easily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols.
SMTP stands for Simple Mail Transfer Protocol. It is an application-layer protocol used for electronic mail (email) transmission. SMTP is a standard protocol that defines how email is formatted and transmitted between servers.
SMPP stands for Short Message Peer-to-Peer. It is a standard protocol for exchanging short messages (SMS) between mobile devices and SMS gateways. SMPP is used by mobile operators to send and receive SMS messages.
In conclusion, HTTP is the protocol that is used for browsing web sites.