A man hammers a wall with elections posters at an open market in Kano, Nigeria, on Friday. The country is preparing for presidential elections on Saturday. President Goodluck Jonathan faces former military ruler Muhammadu Buhari and 13 other candidates in what is seen as the closest presidential race since the end of military rule in 1999. Goran Tomasevic/Reuters/Landov hide caption

itoggle caption Goran Tomasevic/Reuters/Landov

The Grand Ethiopian Renaissance Dam is under construction near Assosa, Ethiopia. When it's completed, the dam will have be able to produce 6,000 megawatts of electricity, making it the biggest hydroelectric power station in Africa. Elias Asmare/AP hide caption

itoggle caption Elias Asmare/AP

Vanilla is seemingly a prima donna spice because its pods have to be hand-pollinated and then boiled and dried in the direct sun for only one hour. iStockphoto hide caption

itoggle caption iStockphoto

It's not the real deal. This Ebola Treatment Unit was set up for a TED talk in Vancouver so people could get a sense of what the units are like, and what it's like to put on the protective suit. Nina Gregory hide caption

itoggle caption Nina Gregory

Light shines through the chlorine-stained windows in the blood-testing area at Redemption Hospital in New Kru Town, Monrovia, Liberia. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

Polina, 37, rests in a hospital bed in St. Petersburg, Russia, in 2011. She is severely malnourished and suffers from numerous diseases, including tuberculosis, hepatitis C and HIV. Misha Friedman hide caption

itoggle caption Misha Friedman

Nigerian President Goodluck Jonathan speaks during the inauguration ceremony of the 750 megawatt power station in the southwestern Ogun state, Nigeria, last month. In an interview with the BBC Friday, he said he hopes to retake all territory seized by Boko Haram within a month. Jiang Xintong/Xinhua/Landov hide caption

itoggle caption Jiang Xintong/Xinhua/Landov