We let $P^n(X,\mathbb{C}) = H^n_o(X,\mathbb{C})$ and $P^{p,q}(X) = H^{p,q}_o(X,\mathbb{C})$ denote primitive cohomology.
My question is why $P^{p,q}(X)\subset P^r(X,\mathbb{R})$, s.t. we can use the basis of $P^r(X,\mathbb{R})$ to represent the basis elements of $P^{p,q}(X)$ (as I highlighted)?
Reference: O'Wells' complex analysis on complex manifold p.208