Грамматика. Помогите, пожалуйста, воткнуть слово в правильной форме.1) The legend tells

Грамматика. Помогите, пожалуйста, воткнуть слово в правильной форме.
1) The legend tells us that about three thousand years B.C. a Chinese Empress, while taking her tea, out of curiosity dipped the cocoon of a silk worm into it and learnt how to unwind the fine thead of silk of which it _______ (compose)
2) It was nearly five thousand years later that a Frenchman, ________ (experiment) with the crushed leaves of the mulberry tree, on which the silk-worm feeds, found out how to produce a fine silk-like filament which we now call artifacial silk.
3) His discovery _____________ (stimulate) other scientistists to search for new fibres, and it was not long before several more were produced.....
4) It is only in the last sixty years that man ______ (succeed) in synthesizing new fibres from inorganic materials.