Q1: What type of circuit is used at the interface point of an input port?

ANS:C - tristate buffer

A latch will hold a logic level that's been clocked into it. It always outputs either a high or a low logic level and continues to output its last state when it's no longer being clocked.

A tristate buffer will output the value that's currently applied to it. It doesn't latch the input in response to a clock. As long as the buffer's 'enable' signal is present, it will output either a high or low logic level. When its 'enable' signal goes false, it will appear as a high-impedance at its output. That's the third state referred to in the term 'tristate' (high-low-disconnected).