Merging two segments is not available or enabled in the shortcut menus! How can I merge?

Hi, I use Trados 2015 and when I wanna merge two segments, first I select two segments by pressing Ctrl and selecting two desired segments, two segments this way became selected but when I right click in the segment number column of the last selected segment, there are no merging option in the shortcut menu! Nevertheless, when I right click on the sentence in the segment there is only "splitting segments" enabled and "merging is disabled.   I know I can only merge neighbor segments in the same paragraph, but something else must be wrong.  

Parents Reply Children
No Data