Which of these were holy Hindu scriptures written by gurus to help connect people to heavenly forces?

To arrive at this answer, you can review each option and eliminate the ones that are not correct.

Option A: the Upanishads - This is a valid option as the Upanishads are considered holy Hindu scriptures that contain teachings and philosophical concepts.

Option B: the Mahabharata - The Mahabharata is an ancient Epic in Hindu literature, but it is not specifically written by gurus to connect people to heavenly forces. It is a story that includes teachings about dharma, but it is not a scripture focused on connecting to heavenly forces.

Option C: the Ramayana - Similarly, the Ramayana is an ancient Epic in Hindu literature, but it is not specifically written by gurus to connect people to heavenly forces. It is a story that teaches virtues and values, but it is not a scripture focused on connecting to heavenly forces.

Option D: the Theravada - This is not a Hindu scripture but rather a branch of Buddhism. Therefore, it is not an appropriate option.

By using the process of elimination, the correct answer is A. the Upanishads.