Answer:
ice age/ Quaternary glaciation
Explanation:
Ice ages have occurred in the earth history and do occur more or less regularly in a cycle. It is believed that ice ages are as a result of small changes in the earth's orbit and also dependent on the solar cycles. The temperatures on the earth reduce causing the ice sheets in the poles to extend to the subtropics. 
 
        
                    
             
        
        
        
Answer:
Cuticle 
Explanation:
Plant cuticle is a waxy covering over the aerial epidermal cells of all the plants. Waxes are composed of cutin and a various organic solvent-soluble lipids. The cuticle is an extracellular hydrophobic layer which provides protection against desiccation and external environmental stresses.  In other words the cucticle helps to retain water and give plants an adavanthe to live  terrestrial life.
 
        
             
        
        
        
Answer:
The correct option is d. it causes exchange diffusion
Explanation:
Amphetamines are synthetic substances with a stimulating effect. Their action lies mainly in increasing synaptic levels of monoamines by various mechanisms, including diffusion exchange through membrane transporters. Amphetamine increases extracellular concentrations of serotonin by displacing the neurotransmitter from its specific presynaptic transporter. When amphetamine binds to serotonin transporters, on the one hand it prevents it from entering the terminal and on the other it reverses the recapture mechanism so that serotonin leaves the synaptic space.