Concept:Joining two cubes forms a cuboid, and its total surface area is given by 2(lb+bh+hl).Explanation:Side of each cube = 10 cm. After joining, length of cuboid = 10+10=20 cm. Breadth = 10 cm and height = 10 cm. Total surface area = 2(20×10+10×10+10×20). = 2(200+100+200). = 2×500. = 1000 sq. cm.Answer:1000 sq. cm, so the correct option is C.