Solution:A Course in General Linguistics (1916) by Swiss linguist Ferdinand de Saussure. It was published after the death of Saussure. It is generally regarded as the starting point of structural linguistics, an approach to linguistics that was established in the first half of the 20th Century by the Prague linguistic circle. One of Saussure's translators, Roy Harris, summarized Saussure's contribution to linguistics and the study of the whole range of human sciences. Saussure's notable ideas are structural linguistics, Semiology, Langue and Parole, Signified and Signifier, Diachrony and Synchronic, Linguistic Sign, Semiotic arbitrariness, Laryngeal theory.
Hence, option (c) is correct.