... 3 than 37°C in April, the hottest month. The division of the season in the north more clearly than in the southern, where the only exception of the highlands, seasonal temperature difference ... full of hills and mountain forests, while the flat land covering about les than 20%. About 40% of mountains, 40% of hill, and its coverring is about 75%. The plains as the Red River Delta, the ... currently the source of sand for cement concrete is ultilize from rivers, sand resources depleted day by day by mining as well as the rapid growth of the construction industry. Therefore the using of...