Question

The following paragraphs are from a draft of an essay about the invention of Velcro.

[1] In 1941, Swiss electrical engineer George de Mestral went on a hunting trip in the Alps with his dog. Upon returning home, he noticed that both his pants and his dog's fur were covered in tiny cockleburs from the burdock plant. Intrigued by how tenaciously they clung to the fabric, he examined them under a microscope. He discovered that the burrs were covered in hundreds of microscopic hooks that caught on the tiny loops of thread in his trousers.

[2] Realizing the potential for a new type of fastener, de Mestral set out to replicate this hook-and-loop mechanism synthetically. After years of experimenting with various fabrics, he found that nylon, when sewn under infrared light, formed stiff loops that could be cut to create hooks. He patented this synthetic replica in 1955 and named it Velcro.

[3] Today, hook-and-loop fasteners are used in everything from apparel and athletic gear to aerospace equipment. NASA, in particular, popularized the product during the Apollo missions, utilizing it to secure objects in zero-gravity environments. Despite its initial rejection by the fashion industry, this Swiss-engineered innovation became a multi-million-dollar global success.

[4] Before the invention could become a household name, however, de Mestral had to convince manufacturers of its utility. The early prototypes were hand-woven and struggled to maintain their grip after multiple uses. It took almost a decade of refining the manufacturing process to produce a fastener that was both durable and cheap to mass-produce.

For the sake of the logic and cohesion of the essay, Paragraph 4 should be placed where?