The correct answer is (a) Sorosis.
A sorosis is a multiple fruit that is formed from a cluster of flowers that are fused together. The mulberry fruit is a sorosis because it is made up of many individual fruits that are fused together to form a single fruit.
A syconus is a type of multiple fruit that is formed from a cluster of flowers that are enclosed in a fleshy receptacle. The fig fruit is a syconus because it is made up of many individual fruits that are enclosed in a fleshy receptacle.
A samara is a type of dry fruit that has a wing-like structure that helps it to disperse by wind. The maple seed is a samara because it has a wing-like structure that helps it to disperse by wind.
A nut is a type of dry fruit that has a hard shell that protects the seed inside. The walnut is a nut because it has a hard shell that protects the seed inside.