The most commonly used diagnostic tool for tuberculosis is a simple skin test, though blood tests are becoming more commonplace. A small amount of a substance called PPD tuberculin is injected just below the skin of your inside forearm. You should feel only a slight needle prick.
The structure has a double bond and an adjacent atom with a lone pair, so it could have resonance. The possible resonance structures are below. The first structure has the most common bonding pattern for all of its atoms, so it is a reasonable Lewis structure.
Homologous Structures. A homologous structure is an organ, system, or body part that shares a common ancestry in multiple organisms. This definition is found in evolutionary biology, and uses the meaning of having a similar structure or origin.