How much does Cauchy-Schwarz Inequality can handle?

Algebra Level 3

Which of the following is the domain of $(a_1,a_2,…,a_n )$ and $(b_1,b_2,…,b_n )$ , such that we will always have

$(a_1^2+a_2^2+⋯+a_n^2 )(b_1^2+b_2^2+⋯+b_n^2 )≥(a_1 b_1+a_2 b_2+⋯+a_n b_n )^2$

Choose the most suitable answer.