Today on The World: Economic worries in China as the country's exports falter; Greece struggles to overcome five straight days of rioting; and Ghana makes moves to become the next big call service center.

The answer to our Geo Quiz today is Kauai, Oahu, Molokai, Lanai, Maui, and the big island of Hawaii. These are Hawaiian Islands where Koa trees grow. Koa wood is used to build some of the world's finest ukuleles. Jake Shimabukoro is a versatile master of the ukulele. He performs on his curly Koa wood ukulele for anchor Lisa Mullins in today's Global Hit.

Female voices may convey more than thoughts and emotion; they may also reveal when a woman is ovulating. A recent German study finds that a woman's voice deepens in pitch at the time she's most fertile. Reporter Ari Daniel Shapiro has the story.

Our daily geography puzzler.

British women of Pakistani descent are sometimes forced or tricked into marrying men back in Pakistan. It's often to help the men secure British visas. But a new law in Britain is giving courts more power to prevent forced marriages. The BBC's Emily Buchanan spends time with some women struggling to get out of forced marriages in Pakistan and some officials trying to help them.

Today President Bush called on Zimbabwe's President Robert Mugabe to step down and end his "tyranny." Zimbabwe is now suffering an outbreak of cholera, among the country's many woes. Anchor Lisa Mullins speaks with Zimbabwean journalist Maxwell John about what life is like now in his country.

Zimbabwe at the crossroads

Anchor Lisa Mullins speaks with cardiologist Bernard Lown. Dr. Lown won the Nobel Peace Prize in 1985 for his work against nuclear proliferation. He's written a new book -- "Prescription for Survival: A Doctor's Journey to End Nuclear Madness."

Lisa Mullins and Dr. Bernard Lown in The World's studios

Spain's construction industry has been hit hard by the country's economic downtown. Now the socialist government there has unveiled a 15-billion dollar economic rescue plan to help get people back on the payroll. The World's Gerry Hadden reports that the plan is part bank bailout-part New Deal.

Anchor Lisa Mullins speaks with former Assistant Secretary of Defense Lawrence Korb about President Bush's speech at West Point today looking back on what's known as the Bush Doctrine.

President Bush delivered a speech today at West Point defending what's come to be known as the "Bush Doctrine." That's his policy of pre-emptive military action. Mr. Bush first outlined his post-9/11 policy in at a speech in West Point in 2002. The World's Jeb Sharp has details.