The correct answer is: A. go out shopping
The phrase “go out shopping” is a phrasal verb that means
to leave home to buy things. It is a common phrase in English and is used in a variety of contexts.The phrase “go out to shopping” is not grammatically correct. The preposition “to” is used to indicate a destination, but in this case, the sisters are not going to a specific place to shop. They are simply going out to shop in general.
The phrase “go out on shopping” is also not grammatically correct. The preposition “on” is used to indicate a journey, but in this case, the sisters are not going on a journey. They are simply going out to shop.
Therefore, the correct answer is: A. go out shopping.