Which type of tissue is defined as being composed of two or more kinds of cells?

The classification of tissues in plants into simple and complex types is essential for understanding their structure and function. Complex tissues are defined as those composed of two or more different types of cells that work together to perform specific functions. This includes vascular tissues such as xylem and phloem, which are involved in the transport of water, nutrients, and sugars throughout the plant.

In contrast, simple tissues consist of a single cell type and serve more basic functions like storage, support, or photosynthesis. Parenchyma is a specific type of simple tissue that comprises thin-walled cells, and transfer tissues are specialized for the transfer of nutrients between different parts of the plant. However, these do not meet the definition of being composed of multiple cell types.

Thus, complex tissues are key to the plant's ability to carry out various physiological processes effectively, making this the correct answer to the question regarding tissue composition.