Concept:Before 1945, Nigeria was under colonial rule, and its main administrative units were provinces.
Explanation:The colonial administration divided Nigeria into provinces, which were used from around 1900.
The country was broadly grouped into the Northern and Southern Provinces, each made up of smaller provinces.
These provinces were then subdivided into divisions and native authorities for local governance.
The regions were only introduced later by the Richards Constitution of 1946, after the period in question.
States did not exist until 1967, when the military government replaced the regions with states.
Therefore, the component units of Nigeria before 1945 were not states or regions but provinces.
Answer:D. provinces