By the same techniques used for genetically enhancing plants, making them disease- or pest-resistant, researchers have been able to increase the amount of protein in potatoes, sweet potatoes, and tobacco.
(a) by the same techniques used for genetically enhancing plants, making them
(b) with the same techniques to genetically enhance plants, so that they are
(c) employing the same techniques used to genetically enhance plants so that they are
(d) employing the same techniques to genetically enhance plants, which makes them
(e) employing the same techniques for genetically enhancing plants that make them