Concept:The word sturdy means strong and firm, so the missing word must mean the opposite: weak or easily damaged.Explanation:Houses built with bricks are strong and solid.Houses built with glass cannot be strong because glass breaks easily.The opposite of sturdy is fragile.The other options do not fit the contrast:Temporary means not permanent, not the opposite of strong.Beautiful and cosy are not opposite in meaning to sturdy.Therefore, the word that correctly fills the gap is fragile.Answer:B. fragile