Answer:
C. Watering hole.
Step-by-step explanation:
Spam attacks are a wide range attack, where by unsolicited or wanted messages are sent to a large group of people. it is used to deliver malicious softwares like virus, trojan horse, rootkit, adware etc.
Adwares are sometimes introduced to an application by the sole programmer of the app, it becomes an attack when sent by intruders for the sole purpose of popping advertisement on the system.
Watering hole is a form on cyber attack meant for a small group of specific people, by oberserving the website used by the group and plants a malware on one or a few of the system.
Typo squatting is another form of cyber attack, where by an attacker squats and waits for a typo error from a user on the internet and attacks from an unsolicited website.