What are the main parts of a cover letter and their purposes? ?

There are 5 parts of cover letter. 1st is the Salutation.  It is the part where you will indicate the name of the person you are writing to. 2nd is the Opening.  This is where you will write your introduction presenting some information why you are pursuing a certain position, and demonstrate your strength. 3rd is the Second Paragraph.  This is where you will define you sample works performance and results achieved. 4th one is the Third Paragraph.  You will indicate here something you know about the company and why you are writing. The last one is the Closing. This is where you will close your letter by suggesting a meeting or by indicating your contact information.

given the options, i would say your best bet is c. the modem supports up to 56 kbps, which is too low for video streaming. dial up modems use actual phone lines, which only can go up to 56 kbps as that's more than sufficient for traditional phone calls. this is also the reason why when a dial-up modem connects, you hear all those sounds. it's literally using the phone line to establish a connection.