Step 1: Understanding the Question:
This question tests knowledge of tree species suitable for block plantations.
Step 2: Detailed Explanation:
Acacia mangium is a fast-growing species commonly used for block plantations.
It is widely planted for timber and pulpwood.
Leucaena leucocephala (B): Used for agroforestry and fodder.
Calliandra callothyrsus (C): Used for fodder.
Cassia fistula (D): Ornamental tree.
Thus, Acacia mangium is the best-known species for block plantations.
Step 3: Final Answer:
Thus, Acacia mangium is the best-known species for block plantations, which corresponds to option (A).
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