At the … of the century, many ways of doing things were introduced.

Analyze the question: You need the word that correctly completes the collocation (a fixed word partnership) with "of the century."

Explain the concept: In English, certain words naturally go together. The phrase "at the turn of the century" is a standard idiom meaning the period when one century ends and another begins (for example, around the year 1900 or 2000).

Test each option:

• A. Sight: "At the sight of the century" makes no sense. "Sight" is about seeing, not time.
• B. Turn: "At the turn of the century" is a correct, well-known idiom that refers to the changeover between centuries. ✔
• C. Event: "At the event of the century" is not an idiom. "Event of the century" can stand alone, but "at the event of" doesn't fit the meaning of a period of time.
• D. Birth: "At the birth of the century" is not a natural expression in standard English. "Birth" is mostly used for people, animals, or ideas, not centuries.

Complete sentence: At the turn of the century, many ways of doing things were introduced.

Tip: For "gap-filling" questions, think about collocations, the words that usually go together. Learn common time idioms like at the turn of the century, at the dawn of a new era, and in the course of time. If a phrase sounds familiar when you say it aloud, it is probably the right one.