1. Fill in the gaps in following sentences:      Sound wave is an                 signal.                      signal can only be 1s or 0s.                      signal can have an infinite number of values between any two values.      External interference affects                 signals but not                 signals.      When several signals are send along the same line at the same time, they are sorted out at the      receiving end by a                .   2. List two advantages other than cost of using digital signals not analogue for transmission of data.