Ex
If you have a mouse.......
1) Highlight the required text in the original post
2) Press the Ctrl and C keys. ( i.e. copy the text) or Right click an select 'copy' from the drop down.
3) Open the Reply box
4) Press the Ctrl. and V keys (print the copied text into the reply box) or right click and select 'paste'
5) Highlight the copied text again
6) Press the "speech balloon" as described already.
QED.