Concept:Option A4 is the open ballot system used in Nigeria during the 1993 elections.
Explanation:The Option A4 model is a voting method in which voters queue openly behind the poster or symbol of their preferred candidate.
This system was first adopted by the National Electoral Commission for the presidential election held on June 12, 1993.
It formed part of the transition programme of the Third Nigerian Republic under the military government of General Ibrahim Babangida.
The open ballot system was introduced to reduce electoral malpractice and make the counting of votes more transparent.
Although the results of the 1993 election were later annulled by the military, the election is still regarded as the freest and fairest in Nigeria's political history.
The Option A4 model was not used in the 1988, 1999, or 2007 elections, as those contests operated under different electoral laws and voting procedures.
Answer:A. 1993 elections