How do you use Mleader Align in GstarCAD?

Align Leader: Aligns and spaces selected multileader objects. After select this option, a prompt message will display > Select a multileader:

For example, selected the Mleaders which content the block A and B. Then select multileader to align. Then select the Mleader which contents the block C. After this, specify the alignment direction (horizontal or vertical).