1 - Choose and opt are basically synonyms. The main differences are that: (1), "opt" has the necessary preposition "for" whereas "choose" doesn't and; (2), "opt" is much rarer to hear in spoken English. 2 - Barren means that nothing is growing in a particular area. It can also be used as an adjective to refer to plants (i.e: a barren fig tree means that the fig tree isn't producing fruit). Arid also means that an area is rather lifeless but has the connotation of being very dry. It can also be used to refer to a climate (i.e: the air can be arid, meaning it lacks water and feels dry). Examples: - A desert is both barren and arid (as nothing grows there and it gets little rain) - A live tree can be barren but not arid (you just can't really describe plants with the word "arid") - The air can be arid but not barren (as it is impossible for the air to grow anything). I'd say that "barren" overall is more versatile and more common. Arid sounds much more technical. 3 - In this case, "single" simply means not being in a relationship and can apply to either a man or a woman. A bachelor only can be used for man (and bachelorette for women). The word bachelor also implies a certain type of lifestyle that merely being single does not. For example, a bachelor typically lives on his own, he doesn't date anyone, he isn't looking to settle down, etc. Being single, on the other hand, is more of a transient state. You can be single in between having different relationships without living a "bachelor" lifestyle. I hope this was reasonably clear!