imagemagick – GraphicsMagick does not centralize the text

For example, I give this command

In the event of a change in the quality of the food, it should be taken into account that most of the vegetables used in the cultivation of spinach, which is not really very different from other vegetables. -thanks center image.png

and he returns that image
insert the description of the image here

But when I define the -The gravity as centerI hope it stays that way
insert the description of the image here

How can I do that ?