1. They do mean the same thing, but aren't perfectly interchangeable grammatically. In your example "all of which" would be correct, but might need commas before and after. "All of them" could be used only if the subject or object of a sentence. For example, if you made the "engines" part of a dependent clause it would work like this, "As for these engines, all of them perform a different function." "All of which" should only be used in dependent clauses. I hope that helps; this is a tricky point! :-) Also, notice that "develops" isn't the right word. And since "engines" is plural, the verb must be "perform" instead of "performs." (I know this is complicated. If you said the wrong phrase, everyone would know what you meant.) 2. You are correct. But, it should be "to protect them" or "so as to protect them," not just "as to." 3. To make something easier. For example, "I decided to tutor Katrine in English to lesson the burden of learning the language." 4. Yes, it means that, but it could also mean that someone was left to do something with no help. "I stopped tutoring students of English, leaving them to shoulder the load on their own." 5. No, Draw tight means to get close in the sense of distance, or to bring someone close to you by pulling them in. Hold tight usually means to cling to something because you are afraid of losing it. 6. That word is not commonly used in that sense. Trait normally means a characteristic. "Katrine's most admirable trait is her eagerness to learn new languages." 10 (?) Breed. It is a verb and a noun, related to each other. A breed (noun) is a genetic type. "The collie is my favorite breed of dog." As a verb, it can mean to mate particular dogs (or other animals) together. "She breeds show dogs as a hobby." Also, "breeding" can be used for people, to denote their family background. "She is a woman of good breeding, from a very prominent family." I hope all of this helps! :-)