You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Cells come in two basic types, prokaryotic and eukaryotic. Which cell structure is found in both prokaryotic and eukaryotic cells?
(A) vacuole (B) nucleoid (C) mitochondrion (D) cytoplasm
D

Plants growing in a pond release a gas that fish need to survive. Which gas do the plants release that fish use?
(A) helium (B) hydrogen (C) nitrogen (D) oxygen
D

How do the spines of a cactus help it survive?
(A) Spines help the cactus get moisture. (B) Spines anchor the cactus in the ground. (C) Spines protect the cactus from animals. (D) Spines support the stems and branches of the cactus.
C