Consider context-free grammars, which of the following statements are true? The left-hand side of a substitution rule can contain terminals. There is exactly 1 start variable. The language generated by a grammar contains variables. A sequence of substitutions, subject to the rules of the grammar, is called a derivation. The set of variable and terminals are disjoint. A rule of the form R E is a valid rule where R is the start variable. Every context-free grammar generates a language that is recognised by a non-deterministic finite state machine