$7($a$)$ Distinguish between principles, guidelines and standards, using examples of each to illustrate. $($b$)$ Why is context important in selecting and applying guidelines and principles for interface design? Illustrate your answer with examples. $7\mathrm{.}8($a$)$ Why are there few effective HCI standards? $($b$)$ How do $$golden rules$$ and heuristics help interface designers take account of cognitive psychology? Illustrate your answer with examples.