We use the OLS estimator in the usual regression model, and the unbiased estimator of variance

We use the OLS estimator βˆ in the usual regression model, and the unbiased estimator of variance σˆ 2. Which of the following statements are true, and why?

(i) cov(β) = σ2(X

X)−1.

(ii) cov(β)ˆ = σ2(X

X)−1.

(iii) cov(βˆ|X) = σ2(X

X)−1.

(iv) cov(βˆ|X) = ˆσ2(X
X)−1.
(v) cov (βˆ|X) = ˆσ2(X
X)−1.