Final answer:
An 'expression' can be a sequence of letters and a sequence of other sequences by combining both elements. In English grammar, expressions can be formed by arranging words and phrases to convey meaning, including poetry and complex sentence structures.
Step-by-step explanation:
An 'expression' can be a sequence of letters and a sequence of other sequences by combining both elements. In English grammar, expressions can be formed by arranging words and phrases to convey meaning. For example, the expression 'I love chocolate' is a sequence of letters that forms a complete thought. Additionally, expressions can also involve sequences of other sequences, such as in poetry or complex sentence structures.