The correct answer is option 'D' - I and II are correct.

Explanation:
I. Buddhist arhats who have qualified themselves to attain Buddhahood in this life, voluntarily forego Bodhisattva state in order to help all their fellowmen to attain that happy state.

Buddhist arhats are individuals who have achieved enlightenment and liberation from the cycle of birth and death. They have qualified themselves to attain Buddhahood in this life, which means they have reached the highest state of awakening and have the potential to become Buddhas. However, instead of pursuing their own enlightenment and leaving the cycle of rebirth, they voluntarily forego the Bodhisattva state. This means that they choose not to enter into the state of a Bodhisattva, which is characterized by the aspiration to attain Buddhahood for the benefit of all sentient beings. Arhats make this choice in order to help their fellowmen, guiding and supporting them on their path to liberation and enlightenment.

II. They receive the same kind of cooperation, respect, and worship as the Buddha himself.

According to Buddhist teachings, the Buddha is revered as the founder of the religion and the ultimate spiritual leader who achieved perfect enlightenment. However, arhats who have reached the state of liberation and enlightenment also receive similar cooperation, respect, and worship from their followers. This is because arhats are considered to have attained the same level of awakening and realization as the Buddha. They are venerated as spiritual guides and role models, and their teachings and guidance are highly valued by Buddhist practitioners.

It is important to note that while arhats and Buddhas are both revered in Buddhism, there are differences between the two. Buddhas are considered to be fully awakened beings who have attained perfect enlightenment and have the ability to teach others the path to liberation. Arhats, on the other hand, have achieved personal liberation and enlightenment but may not possess the same level of wisdom and compassion as Buddhas. Nevertheless, arhats are still highly respected and regarded as important spiritual figures within the Buddhist tradition.

III. Bodhisattva is a conception of the Hinayana school of Buddhists.

This statement is incorrect. The conception of Bodhisattva is not limited to the Hinayana school of Buddhism. The idea of the Bodhisattva path, which involves the aspiration to attain Buddhahood for the benefit of all sentient beings, is central to Mahayana Buddhism. In Mahayana Buddhism, the Bodhisattva ideal is highly emphasized, and practitioners strive to cultivate the qualities of compassion, wisdom, and skillful means to help alleviate the suffering of others. The Hinayana school, also known as Theravada Buddhism, focuses more on individual liberation and the path of the arhat, although it still acknowledges the existence of Bodhisattvas.

In summary, the correct statements are I and II. Arhats voluntarily forego the Bodhisattva state to help others, and they receive the same kind of cooperation, respect, and worship as the Buddha. Statement III is incorrect as Bodhisattva is a conception of Mahayana Buddhism, not just the Hinayana school.

1 and 2 are corect