Maths for Economics question

(3) Given the well-behaved production function Q(L,K) = ALK", (A,a,b > 0), which of the following statements is correct? 1. The elasticity of substitution is always constant but its value depends on the size of A. ii. The elasticity of substitution is 1 only if a + b = 1- iii. The elasticity of substitution is always 1. iv. The elasticity of substitution is always -1. v. None of the above are correct