You are presented with the quiz "starfish lack what kind of system?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "echinoderms lack respiratory and excretory systems" and "echinoderms are represented by the starfish". So, what's the best answer to the question?
OPT:
[1]. respiratory;
[2]. critical organs;
[3]. alveoli;
[4]. heat or cold;
[5]. hydration;
[6]. Bodily water;
[7]. food and shelter;
[8]. frontal zones;
[1].