Multi-select problem: How does the next paragraph end?

How to retain knowledge
Use spaced repetition.
If you want to remember something, don't repeat it over and over to yourself-this is known as massed repetition. Instead, let some time elapse before you repeat it.

OPT:
[a]. To ensure you haven't depleted your memory beyond 20 minutes, try counting about ten (you really shouldn't) for no more than five minutes each day. When twenty minutes have passed, move on to the next thirty-five minutes.;
[b]. Ideally, you want to try to retrieve the information exactly at the moment when you were about to forget it. The difficulty of retrieving the information correlates to how strongly you will remember it.;
[c]. For example, if you are memorizing a presentation, pause and think " wow, i missed that presentation. Let's go back for it later " and no longer repeat it; this will still make it harder for you to remember information.;
[d]. This will help you retain the information all at once and can also make a much more significant impact on the learning process. Practise this practice the next day or every third day until you've become a better learner.;
[b].