On a dark gray blackboard, many mathematical formulas are written in chalkOn a dark gray blackboard, many mathematical formulas are written in chalk
Lecture with formulas on the blackboard in front of studentsLecture with formulas on the blackboard in front of students
A woman with a telescope in a leather uniform on board an airshipA woman with a telescope in a leather uniform on board an airship
The american multi-purpose fighter f 16 has weapons on boardThe American multi-purpose fighter f 16 has weapons on board