[solved] how to select from one group of breps, each containing different number of breps?

Suppose I have three brep components A, B, C, each containing different number of breps inside, e.g. A contains breqs a1, a2, a3; B contains b1, b2, b3; C contains c1, c2, c3 ...

How to use number slider and a list item component to select a particular brep A or B or C, without selecting a particular breq inside each of them?

It seems the merge function will merge all the breqs inside each of the breps into one flattened list ...