What does the word “their” in paragraph 3 refer to?

Read the following passage and mark the letter A, B, C, or D to indicate the correct word or phrase that best fits each the numbered blanks.

In an educational context, the term ‘learner independence’ has gained increasing importance in recent years. It is of particular (26) _______ to language learning and commonly refers to the way students confidently control and organise their own language learning process. While some people seem to have an almost instinctive flaw for languages, (27) _______ have to rely on strategies to maximise their skills and learn a foreign language more effectively.

The main thing to remember is that becoming a truly independent learner ultimately depends above all on taking responsibility for your own learning and being prepared to take every opportunity available to you to learn. You also increase your chances of (28) _______ by learning according to your own needs and interests, using all available resources. Research shows that learners (29) _______ adopt this approach will undoubtedly manage to broaden their language abilities considerably and, (30) _______,  are mote likely to achieve their objectives in the longer term.

                                  (Adapted from “Complete Advanced” by Laura Mathews and Barbara Thomas)