Which option is a good example of co$-$presence?

a$.$

Podcasts are used to stream audio$-$based lectures to distance education students

b$.$

Video and sound with fixed cameras and microphones are used for staff meetings where the participants are working from home during the COVID$-19$ pandemic

c$.$

In a large computer lab with partitions between each student, the face of a student who is participating in a discussion is projected on all the computer screens in all the booths.

d$.$

A roaming robot that can hear and talk, represents a conference attendee $($who is in quarantine$)$ during a networking session in teatime.