Final answer:
The stylist can use the feed-in technique to add extensions to single braids, resulting in a seamless and natural-looking braid.
Step-by-step explanation:
To add extensions to single braids, the stylist can use the feed-in technique. This technique involves gradually adding synthetic or natural hair extensions to the braid as it is being formed. This is done by starting with a small section of the natural hair and beginning the braid, then slowly feeding in small pieces of the extension hair to make the braid thicker as it gets longer. The result is a seamless and natural-looking braid that has been extended in length. The key to this technique is to add the extension hair subtly so the transition from natural hair to the extension is nearly undetectable.