The stats command is used to calculate summary statistics for your search results such as count, sum, avg, min, max and more2. The stats command supports various functions that you can use to perform calculations on your fields2. However, addtotals is not a stats function but a separate command that adds a row or column with the total of the values in each group2. Therefore, option B is correct, while options A, C and D are incorrect because they are valid stats functions.

The relationship between data models and pivots is that data models provide the datasets for pivots. Data models are collections of datasets that represent your data in a structured and hierarchical way. Data models define how your data is organized into objects and fields. Pivots are user interfaces that allow you to create data visualizations that present different aspects of a data model. Pivots let you select options from menus and forms to create charts, tables, maps, etc., without writing any SPL code. Pivots use datasets from data models as their source of data. Pivots and data models are not the same thing, as pivots are tools for visualizing data models. Pivots do not provide datasets for data models, but rather use them as inputs.
Therefore, only statement A is true about the relationship between data models and pivots.

The Splunk Common Information Model (CIM) is a collection of data models that apply a common structure and naming convention to data from any source. A data model is a type of knowledge object that defines the structure and relationships of fields in a dataset. A data model can have one or more datasets, which are subsets of the data model that represent different aspects of the data. For example, the Network Traffic data model has datasets such as All Traffic, DNS, HTTP, etc. The CIM contains 28 pre-configured data models that cover various domains such as authentication, network traffic, web, email, etc. The CIM is implemented as an add-on that contains the JSON files for the data models, documentation, and tools that support the consistent, normalized treatment of data for maximum efficiency at search time23
1: Splunk Core Certified Power User Track, page 10. 2: Splunk Documentation, Overview of the Splunk Common Information Model 1. 3: Splunkbase, Splunk Common Information Model (CIM) 2.

The timechart command is used to create a time-series chart of statistical values based on your search results2. You can use the timechart command with a by clause to split the results by one or more fields and create multiple series in the chart2. However, you can only list one field after the by clause when using the timechart command because _time is already implied as the x-axis of the chart2. Therefore, option B is correct, while options A, C and D are incorrect.