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Option C, Analogous Organ

Explanation:

Thorns and spines are analogous organs. Analogous organs are those which have different function but have similar look and structure.  

Thorns are basically modified stem and spines are modified leaves. Both the thorns and spines are different in structure but they have same function which are as follows -  

a)They control the rate of respiration

b)Provide protection to the plants