$\"\"$ and point (1, 1, 1).

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

(b). The adjacent edges of parallel piped are $\"\"$ .

\

$\"\"$

\

$\"\"$