I want to buy _________ piano for my daughter as the birthday gift. She's good at playing ________ piano. What do you think of _________ black one?
A:a, the, a
B:a, /, the
C:a, the, the
D:the, /, a
水绵和衣藻同属藻类的主要原因是( )
蚯蚓在土壤中生活,以腐烂的植物为食,所以,蚯蚓在生态系统中相当于( )