Answer: C. Compound object.
Explanation: Generally, a sentence is formed with 3 elements:
- Subject: tells who or what it is about;
- Verb: shows what the subject is doing or is;
- Object: object or person, which receives the action of a verb;
Compound is a word for two or more of something.
The combined sentence above uses a compound object, in other words and in this case, two objects that receives the action of the verb: "months of preparation and detailed planning" are two objects that realtes to the verb in past tense "took".
