Answer:
Secondhand smoke is the combination of smoke from the burning end of a cigarette and the smoke breathed out by smokers. Secondhand smoke contains more than 7,000 chemicals. Hundreds are toxic and about 70 can cause cancer.
Explanation:
It is harmful too
 
        
             
        
        
        
Answer:
All medicines must be stored in a cool, dry place, away from sunlight and moisture. Some medicines require special storage conditions such as in the refrigerator, or even the freezer. Such medicines can expire quickly if they are improperly stored at room temperature, becoming toxic or less effective.
Explanation:
 
        
             
        
        
        
Answer:
This is achieved because the sodium channels have a refractory period following activation, during which they cannot open again. This ensures that the action potential is propagated in a specific direction along the axon.
 
        
                    
             
        
        
        
Answer:
d. left ventricle
Explanation:
Heart consists of four chambers: left atrium, right atrium, left ventricle and right ventricle. The atria are located above the ventricles and their function is to  pump blood to the ventricles. 
Right ventricle pumps the deoxygenated blood to the lungs via pulmonary artery. Pulmonary vein brings back oxygenated blood from lungs to the left atrium. From here the blood is sent to left ventricle. Left ventricle pumps blood to the entire body via aorta. Since it has to make blood reach to every part of the body from head to toes, it generates maximum pressure. Therefore, left ventricle also has thickest heart muscles.