Which of the following is not a common operation of MindSpore?

The correct choice indicates that "signal" is not a common operation of MindSpore. MindSpore is a deep learning framework developed by Huawei that supports various operations and functionalities for building and training machine learning models.

The "nn" module within MindSpore refers to neural network functionalities, facilitating the creation and management of various neural network architectures. The "array" module typically involves tensor manipulations, which are fundamental for data representation in machine learning. "math" encompasses mathematical operations that are essential for performing calculations during model training and evaluation, including operations on tensors and other numeric data.

In contrast, "signal" does not represent a primary focus or operational capability of MindSpore. While signal processing might be relevant in specialized applications of AI, it is not a core component typically highlighted within the MindSpore framework's standard operations as compared to the other options that are essential for building neural networks and conducting mathematical computations. This distinction clarifies why "signal" is the correct answer.