Which Greek letter is equivalent to the English letter 'T'?

The Greek letter that is equivalent to the English letter 'T' is indeed the letter Τ (Tau). In the Greek alphabet, each letter has a corresponding sound and shape, and in this case, Tau is directly represented as the letter 'T' in English both phonetically and visually.

This correspondence is important in various fields, including mathematics and science, where Greek letters are often used as symbols to represent variables or constants. For example, Tau is sometimes used to represent torque or time constants in physics. Its resemblance to the English 'T' makes it easier for those familiar with both alphabets to relate the two forms.

In analyzing the other choices, while Υ (Upsilon) represents a sound closer to 'U' in English, and Σ (Sigma) corresponds to an 'S' sound, T itself is a direct representation in the form of the letter 'T', which is why it is not the correct choice. The letter T in the options is simply the English letter and does not relate to the Greek alphabet. Hence, the option that truly represents the Greek equivalent of the English 'T' is Tau, Τ.