The main argument against the 1999 Constitution is that

Analyze the question: The question asks for the main criticism of Nigeria's 1999 Constitution.

Explain the concept: The 1999 Constitution came into force on 29 May 1999, when Nigeria returned to civilian rule. It was drafted by a panel set up by General Abdulsalami Abubakar's military government, and it was promulgated as a decree (Decree No. 24 of 1999). It was not drafted by elected representatives, and it was not put to a referendum. As a result:

• The Constitution's opening words, "We the people of the Federal Republic of Nigeria...", are widely criticised as inaccurate, because the people did not actually make it.
• Critics argue it lacks legitimacy and popular participation.
• This is why there are continuing calls for a Sovereign National Conference and for constitutional review.

Step-by-step evaluation of the options:

• A. It was imposed by the military: This is the most widely cited and fundamental criticism. The document was handed down by the military rather than made by the people. ✔
• B. The executive has an immunity clause: Section 308 does give immunity to the President, Vice-President, Governors and Deputy Governors. This is a valid criticism, but it is a specific provision, not the central objection to the whole document.
• C. It is expensive to operate: This is a criticism of the presidential system's cost, not the main argument against the Constitution itself.
• D. It did not create additional states: The Constitution retained the 36 states, but this is a minor complaint and not the main argument.

Answer: The main argument against the 1999 Constitution is that it was imposed by the military, so the correct option is A.

Exam tip: For "main argument/criticism against a constitution" questions, think about its origin and legitimacy first. Remember: "1999 = Military-made, not people-made." Questions on this topic often link to the phrase "We the people" and the calls for restructuring.