6. For each of the following strings, state whether it can be derived from the rules of the grammar of Figure 7.5. If it can, draw the corresponding syntax tree:

*

(a) a + ( a )

(b) a * ( + a )

(c) a * ( a + a )

(d) a * ( a + a ) * a

(e) a + ( - a )

(f) ( ( ( a ) ) )