如何将Bootstrap卡中的图像设置为相同的高度/宽度？

So here is my code, it displays 6 cards, three across and two rows. I would like for the images to all be the same size without having to manually resize the images. The responsiveness does work, i use "img-fluid" as a class and when i go to a mobile or smaller browser, they all have the same width, but the height is still off. So here is my code, it displays 6 cards, three