1.1. Several syntax diagrams are shown.

State why each number is invalid for the given syntax diagrams.

21

Reason ..................................................

123

Reason ..................................................

1.2. Complete the Backus‑Naur Form (BNF) for the given syntax diagrams

::= ....................................

::= ....................................

1.3. A new syntax rule, code, is required. It must begin with a letter, followed by one or two numbers, and end with a symbol.

(i) Draw a syntax diagram for code.

(3)

(ii) Write the BNF for code.

(2)