4. by my
Prepositions can be difficult in English if you are a non-native speaker. They are words that show a relationship or connection between two other words. It's important to remember that in English, the order in which words are placed is all-important for determining meaning. To put it another way, you usually can't tell how words relate to each other by their endings, but must rely on where they are placed in the sentence. For example, "Cathy came after Alfred in the line" means the opposite of "Alfred came after Cathy in the line." The preposition "after" and the placement of the names are important in determining the meaning of the sentence.
Because prepositions can sound interchangeable to a non-native speaker, it is important to read as much English as possible and to listen carefully to how people in your location speak in order to learn the correct use of prepositions--and in the meantime, not to worry too much while you are learning!