This is an exercise that will help you learn the differences between frequently confused words. We call them "Appropriate Words" sentence completion exercises because the key thing to learn here is the appropriate context in which you should use these words. Sometimes you can use both words, but one answer is more appropriate to use in that context. For other sentences, one word is the only possible answer. The explanations at the bottom of each page will clarify all of the answers if you're not sure about certain sentences.
An explanation of the answers:
1. "To teach" and "to lecture" may seem nearly interchangeable in all situations, but, in this context, lecture is the correct answer. When you tell someone what to do in a "bossy" or authoritative way, you are lecturing them.
2. Classes and lessons may also seem interchangeable. There is practically no difference between Skype English classes and Skype English lessons, for example (at least in the way we define it). However, "to teach someone a lesson" has a specific meaning. It means to discipline them in some way so that they don't make the same mistake in the future. In this case, the boy's mother wanted to teach the boy that it is not OK to play video games when he should be studying.
3. While you may be similar to people in your family, the proper word to use in this context is related. You are related to people in your family.
4. Although climate and weather both refer to the conditions outside, they have very different meanings. The weather means what the conditions will be at a specific time. Climate means the long term conditions of a particular place. Since the sentence in number 4 is referring to the conditions for a single day, weather is the more appropriate word to use here.
5. Opponent and enemy both refer to people who are against you. However, opponent is a much milder term. Your best friend or husband or wife, for example, could be your opponent while playing a friendly board game. An enemy, on the other hand, is a person who is hostile towards someone else. Your enemy doesn't wish for good things to happen to you. Since this sentence is about politicians, the best answer is opponent. Most politicians don't wish harm to their colleagues. After an election they usually continue working together in a constructive and friendly way.
6. If you are showing someone how to do something (like tying their shoes), this is generally referred to as teaching. A lecture is usually more formal and lasts for a long period of time.
7. Again, lessons and classes mean nearly the same thing. But if you are referring to a group of students, it's only appropriate to use "class." For example: "The teacher said hello to the class."
8. Simply put, similar means to have an appearance or quality that resembles something else without being identical. Related is when something has a relationship with something else--they don't have to be similar, necessarily. For example, raccoons and bears are related (biologically speaking), but they are not similar. They have a different size, appearance, etc. Since number 8 is about words that resemble one another, the better answer is "similar."
9. Since this sentence is about worldwide conditions over a long period of time, "climate" is the correct answer here.
10. It would be very severe if someone hated you and wanted to destroy your culture. Therefore, enemy is the correct answer here. An enemy is someone who harbors ill intentions towards you.