The correct answers are A) mosques and D) libraries.
Architects and builders were brought to Timbuktu to build mosques, libraries, and other public buildings.
For instance, they did a great job of building the Mosque of Djenne. They use adobe as the main construction material. Another important building was the University of Timbuktu. These works of architecture were developed in times of the Ghana kingdom, that make a priority the construction of important public buildings.