Symplectic mean curvature flows in K\"ahler surfaces with positive holomorphic sectional curvatures

In this paper, we mainly study the mean curvature flow in K"ahler surfaces with positive holomorphic sectional curvatures. We prove that if the ratio of the maximum and the minimum of the holomorphic sectional curvatures is less than 2, then there exists a positive constant $\delta$ depending on the ratio such that $\cos \alpha \ge \delta$ is preserved along the flow.