How do only certain cells respond to particular signaling molecules that may be sent throughout the body? see section 11.3 ( page 244) ?

Not all cells have the ability to receive signal from other cells and respond to those signals. There are certain cells that have specific receptors (receptor proteins) attached on their cell surface. These receptors are specific for some signal molecules. When the signal molecule attaches to the receptor of the cells, the signal is received and carried forward. This cell to cell signaling is called signal transduction or cell signalling. 

The answer is b. hope this !