1) in stop and wait arq, if data 1 has an error, the reciever sends ... a frame

nak 0

nak 1

nak 2

nak

2) at the crc checker, if the remainder is ... then the data unit is damaged

a string of 0s

a string of 1s

a string of alternatins 1s and 0s

not a string of 0s

3) ... is a controlled access method

slotted aloha

pure aloha

csma/cd

token passing