The Gaia hypothesis believes that the living and non-living bodies of the Earth form a complex system that can interact with each other. This hypothesis is divided into a strong Gaia hypothesis and a weak Gaia hypothesis. Among them, the weak Gaia hypothesis holds that various organisms on the earth effectively Regulates the temperature and chemical composition of the atmosphere. While the organism affects the biological environment, the environment also reflects the process of biological evolution. The strong Gaia hypothesis further believes that the earth is a huge organism with the ability to self-regulate. The health of the organism can even eliminate those harmful factors on its own. According to the above definition, the weak Gaia hypothesis among the following options is:. ['the use of solar energy by the earth is a kind of metabolism on a planetary scale.', 'the ozone hole in the atmosphere is caused by human overactivity.', 'the introduction of heat-resistant plants in the desert has promoted the development of local tourism.', 'the importance of environmental protection is that the earth is the only planet suitable for human habitation.']