Consider the following sentences : (a) when the hunter saw the tiger, he climbed up a tree. (b) on seeing the tiger, the hunter climbed up a tree.

• A. (a) is simple sentence and (b) is compound
• B. (a) is compound sentence and (b) is simple
• C. (a) is complex sentence and (b) is simple
• D. (a) is simple sentence and (b) is complex