Techniques of making silk were first invented in China around _____ years ago.

Correct option is D

Techniques for making silk were first invented in China around 7000 years ago. Though, the earliest evidence of silk dates back to more than 8,500 years ago and has been found in the early Neolithic Age tombs of Jiahu, China.
The process of silk production is known as sericulture. The Chinese guarded the secret of silk production for thousands of years, exporting only the finished product.
The use of silk within China was not confined to clothing alone, and silk was used for a number of applications, such as writing.
Silk was cultivated in Japan at least before AD, and, by 552 AD.