Canopy refers to the dense leafy tops of the tall tropical trees that are around 50 to 80 meters above the ground level. Therefore, option (a) is correct.
Niche is often referred to as the occupation of the organism and takes into account the explanation about organism’s position in the food web and its role. In simple terms, it is the role of the organism towards the ecosystem. Therefore, option (b) is incorrect.
Taiga is the dense evergreen forest of coniferous trees present in the temperate zone. Therefore, option (c) is incorrect.
Understory refers to the smaller and shorter trees that are present in the shade below the canopy. Therefore, option (d) is incorrect.
Hence, in a tropical rain forest, the dense covering formed by the leafy tops of tall trees is called the (a) canopy.