When you "astound" someone, you surprise that person. An astounding fact is one that is surprising or marvelous. Now, you might think that "irregular" or "unusual" are potential correct options. Yes, irregular/uncommon things are surprising because of their irregularity; however, the words do not mean "astonishing." There are some irregular/uncommon things that are not astounding—like irregular drops of water and uncommon colors of t-shirts.

The word "moderate," when used as an adjective, describes something that is not extreme in its quality or nature. A moderate thing is neither too excellent nor too horrible. It is "in the middle." When we make moderate demands on someone, we make demands that are not too large nor too small. Thus, they are "reasonable" (in the sense that they are "understandable" because they are not too extreme). This is the only option that expresses this idea of being in the middle and not too extreme.

The verb "to astound" means "to amaze." When something is described as being "astonishing," it is amazing. Thus, we could say, "It was astonishing how quickly John made progress at learning to play the organ. In only two years, he was more skilled than most people who had taken twenty years of lessons."

When we "stun" someone, we stop him or her from acting. Sometimes, violent actions can do this. If someone punches another person very hard, that person can become stunned and unable to move; however, something that is very beautiful or amazing can also stun someone. You have likely heard something like, "The view of the mountains was stunning. Edward had to stop and stare at them." It is in this sense that the word is being used for this question.  Thus, the best option is "amazing." Something that is "stunning" is sometimes (maybe often) amazing.

When two things are "similar," they are very much alike; however, they are not completely alike. When two things are 100% alike, they are equal or, simply, "the same." The word "similar," however, refers to things that are alike without being exactly the same. For instance, two cups could be similar in shape, though they are each a little bit different. Likewise, two shirts might have similar colors, though they are not exactly the same as each other.

A "talent" is a skill or ability that someone has. For example, the ability to play the tuba very well could be said to be a particular talent. We would describe such a person as saying that he or she is a "talented tubist." Thus, the best option among those given is "skilled." When we call someone a "skilled pianist," we mean that he or she is talented at the piano. Now, while such a person may be famous and, perhaps, even rich, being talented means being skilled. The fame and wealth come later if the person is lucky; however, no matter what, he or she will be skilled so long as he or she is talented.

When something is intriguing, it draws your interest. It does not have to be famous or well known. It just needs to be something that is rather interesting. For example, a mysterious doorway with a weird light coming out of it might be called "intriguing". The word "fascinating" is a close synonym for "interesting." Therefore, it is the best option among those given.

The word "abnormal" can be understood from its parts. The "ab-" prefix means away from or even not. Thus, something that is "abnormal" is not normal. When something is unusual, it is not usual. Such a thing does not have to be amazing. For example, every stone in a driveway may be brown. Then, if one is black, it is abnormal. That certainly is unusual for the driveway. It is not, however, amazing!

Whenever we say that we "admire" someone, we mean that we have a very high opinion of that person. We respect such people for who they are and for what they do. Although such persons are sometimes famous, often they are not. We admire our grandparents, even if few people know them. This means that we respect them, and thus "respected" is the best option.

When something is "luxurious," it is expensive and often unnecessary. When we speak of "luxuries," we are often speaking of items that we do not need, though we want them. For example, a very expensive car is a luxury item. We buy it because it is magnificent and wonderful, not merely because it is something that we need. Hence, the word "luxurious" can mean "magnificent" because such luxurious things tend to be very grand.