The correct option is A of / at
Here, 'of / at' is correct because 'of' is used to say what somebody/something is, consists of, or contains, here it is lemonade. 'At' is correct because it is used to say where something/somebody is, here it is the shop.
'At / of' is incorrect because 'at' is used to say where something/somebody is and 'of' is used to say what somebody/something is, consists of, or contains.
'From / at' is incorrect because 'from' is used to show where somebody/something starts and 'at' is used to say where something/somebody is.
'From ' of' is incorrect because 'from' is used to show where somebody/something starts and 'of' is used to say what somebody/something is, consists of, or contains.