Hi Akram. Firstly, "the" is for something very specific and here we are talking about education and investment in general. The use of "ing" is because it is an activity. Another example is, "I like painting" - the activity. I hope that helps. Keep practicing.

You can use the present participle ("unlocking") or the infinitive ("to unlock"). In your example, it makes little difference which one you use. However, they do "feel" different. Use infinitives to state facts or to be exact. Use present participles to paint pictures, to be descriptive, or to be imaginative. Let me give you an example where it would make a big difference. Consider this sentence in which Jim says: "Jack, you have three keys on your keychain. Which one is the key to unlock your front door?" If Jim had said "to unlocking your front door" it would have sounded strange. Jim is asking a specific question. He wants a specific answer, not a description. He wants the facts. The infinitive serves that purpose well.