What do they have in common? | 找找共通點

Inspired by NPR's Sunday Puzzle, I have created some Cantonese-English word puzzles. 

Your job is to figure out what is in common with the list of words I provide. 

NPR SP's example was "tom, alley, copy" = CAT (tom cat, alley cat, copycat)

To make this more challenging, the puzzle is in English, but the answer is in Cantonese. 

哩一堆字用廣東話講有咩共通點？（每個答案字數都係一）

1. phone, basketball, swing
2. water, electricity, plane
3. rope, bottom, joint
4. skin, mountain, soldiers

Bonus: If you are feeling super smart, go ahead and name an additional item that fits the pattern for each puzzle. 

係醒目既不妨試吓每一題再諗多一個例子！

Have fun! 

[DON'T SPOIL THE FUN ALERT] Please do not post your answers if you know them! Let others have a chance to guess first :)