a) Hadoop is an ideal environment for extracting and transforming small volumes of data
b) Hadoop stores data in HDFS and supports data compression/decompression
c) The Giraph framework is less useful than a MapReduce job to solve graph and machine learning
d) None of the mentioned

Answer: b
Explanation: Data compression can be achieved using compression algorithms like bzip2, gzip, LZO, etc. Different algorithms can be used in different scenarios based on their capabilities.