Final answer:
Ferdinand de Saussure was significantly influenced by structural grammar, which aligns with his linguistic theories of langue and parole.
Step-by-step explanation:
Ferdinand de Saussure, a Swiss linguist, is known for developing the field of structural linguistics. In his view, language comprises of a system of signs that express ideas, suggesting that the meaning is derived from the relationship between these signs rather than from the signs themselves. Saussure proposed that language has two aspects: langue, the abstract system of rules and conventions, and parole, the practical use of language in concrete situations. This duality is a foundational tenet of his linguistic theory. Saussure's study was greatly influenced by structural grammar, which focuses on understanding the rules and patterns underlying the structure of language.
The proper answer to the question is (d) Structural grammar.