Final answer:
In English, when 'the' is the first word in a sentence, it is referred to as the definite article and not considered the key unit. The definite article specifies a particular noun and is not case-sensitive. It is a fundamental part of English grammar.
Step-by-step explanation:
In English, when the word 'the' is the first word in a sentence, it is not considered the key unit. Instead, it is referred to as the definite article. The definite article is used to specify a particular noun and is a fundamental part of English grammar. Unlike other words in a sentence, the definite article is not case-sensitive and cannot be differentiated in spoken language.