Nice info but isn't a rule to join independent-dependent clauses using sub-ordinating conjunctions OR relative clause. 2 clause here areAs to your "which" question regarding choices (D) and (E), in fact, the relative pronoun is not necessary. In fact, we very often use adjective clauses without relative pronouns in English, with no comma separating them from the term they're modifying. For example:
That story you wrote was very good.
Here "you wrote" is an adjective clause describing "story." While it might be clearer (especially in the case of a long relative clause, such as in the above OG question) to include a "that" before "you wrote," it's not required. If set off my commas, though, you'll always see a relative pronoun, most likely "which:"
That story, you wrote, was very good (wrong)
That story, which you wrote, was very good (right)
>>> the company has become increasingly willing to compete for the mass market sales (independent)
>>> it would in the past have conceded to rivals (dependent)
