Answer: At least one notebook library to be executed

When creating a new Delta Live Tables pipeline, the essential requirement is to specify at least one notebook library to be executed. Delta Live Tables pipelines are defined using notebooks or Python files that contain the pipeline logic. The other options are not mandatory: - **A. A key-value pair configuration**: Configuration settings are optional and can be used to customize pipeline behavior but are not required. - **B. The preferred DBU/hour cost**: Cost settings are optional and can be configured but are not mandatory for pipeline creation. - **C. A path to cloud storage location for the written data**: Storage locations can be configured but are not required; Delta Live Tables can use default storage locations. - **D. A location of a target database for the written data**: Database locations can be configured but are not mandatory; default databases can be used. The fundamental requirement is that a pipeline must have source code (notebooks or Python files) to execute, making option E the correct answer.

Author: Keng Suppaseth