What does ob in front of a date mean?

What types of landforms are found in the Sahara Desert? How many workers are employed for the construction of the Leaning Tower of Pisa? What tourist attraction begins with L? Why is a zookeepers job important? What is st. johns physical region? How long does it take alain to climb the Burj Khalifa in Dubai? Is the windsor hotel haunted? Muscat is the capital? Who named the Mississippi Valley and ldquoLouisiana and? What type of bridge the Brooklyn bridge? Are the rocky mountains younger than the Appalachian mountains? Is the Hoover Dam construction finished? What is the name of the large city near the southwestern end of Lake Superior? Are there any historical places named after Ludwig Leichhardt? Why are temperate forest called decididuous? Why was Canyonlands established? What are the forces involved in roller coasters? How far is Grand Canyon from Oklahoma City? What was the name of the castle that gave he-man his powers? What is the highest mountain on earth and its elevation in feet?