Final answer:
Sqoop (Option A) is the Hadoop ecosystem tool used for transferring data between relational databases, such as DB2 and MySQL, and the Hadoop cluster. It is a command-line application that supports import and export functions between Hadoop and external databases.
Step-by-step explanation:
The Hadoop ecosystem tool that can import data into a Hadoop cluster from databases such as DB2, MySQL, or others is Sqoop (Option A). Sqoop is a command-line interface application that is designed to transfer data between Hadoop and relational databases. You can use Sqoop to import data from a relational database management system (RDBMS) such as MySQL or Oracle into the Hadoop Distributed File System (HDFS), Hive, or HBase. Additionally, Sqoop also allows exporting data from Hadoop to external relational databases. To import data using Sqoop, one would typically execute a command that includes the source database connection parameters, the target destination within the Hadoop ecosystem, and possibly other options to refine the data import process, such as selecting specific columns, controlling the number of parallel tasks, or specifying import conditions.