a) static equilibrium equations are insufficient for determining internal forces and reactions on that structure
b) static equilibrium equations are sufficient for determining internal forces and reactions on that structure
c) structure is economically viable
d) structure is environment friendly

Answer: a
Explanation: When the static equilibrium equations are insufficient for determining internal forces and reactions on that structure, the structure is said to be statically indeterminate. Analysis of these structures is complex and cannot be analysed only by using laws of statics, various analytical methods like slope deflection method, moment distribution method, etc.