Presence indicators . a. are small digital badges that people can embed in emails and on websites to share their contact information and social affiliations.
b. are visual elements used to change the aesthetic of a web page.
c. are things that others create we feel are worth redistributing to our social networks.
d. are an option to have one's profile reflected back to them from the perspective of others.
e. enable users to project an identity more vividly to others within a community

One of the scarce resources that constrain our behavior is time. each of us has only 24 hours in a day, and we must allocate our time in a given day among competing alternatives. how do you go about allocating your time in a given day among competing alternatives? how do you go about weighing the alternatives? once you choose a most important use of time, why do you not spend all your time on that activity? a. as more and more time is spent on one activity, the opportunity cost of that activity in terms of other activities rises. b. as less and less time is spent on one activity, the opportunity cost of that activity in terms of other activities rises. c. as more and more time is spent on one activity, the opportunity cost of that activity in terms of other activities falls. d. b and c only.