Which of the following are risks to a network? a Sending emails
b. Granting administrator access to a non-administrator
c. Opening files from unknown senders
d. Unwanted advertisements

option  b and c are correct answers.

Explanation:

Let see each option in detail.

a) Sending email is not a risk.

b) Granting access is a problem because the other person can undermine the network

c) Unknow senders can send virus or other malicious code to corrupts you data.

d) Unwanted advertisement is not a big deal.

i belive the answer you are looking for is d: the nether

answer(igmp);