Answer the questions at the end based on the text.

(CNN) -- It's been more than three weeks since militants from the dreaded Boko Haram terrorist group dragged 276 girls out of their beds at a boarding school in northern Nigeria, and still no one knows where the girls are. International assistance has begun to flow into Nigeria, whose president has vowed to end the terror threat plaguing his country.

Here's what you need to know to get caught up:

Where are the girls?

It's anyone's guess. Boko Haram's leader, Abubakar Shekau, said in a video that he was going to sell them into slavery, but it's unknown whether he has. Pentagon spokesman U.S. Navy Rear Adm. John Kirby and other officials have said they believe the girls may have been separated into smaller groups, making the task of finding them inordinately more difficult. Gordon Brown, a former UK prime minister and the U.N.'s special envoy for global education, speculated that the girls may have been moved into neighboring countries. "The search must be in Niger, Cameroon and Chad, to see if we can find information," he said.

What's being done to find them?

Nigeria hasn't given a lot of information about its efforts other than to say that its soldiers have been out in the field, looking for the girls. Nigerian police offered a $310,000 reward, but there's no evidence that has turned up any leads. The United States and Britain have sent advisers to help the Nigerian government find the girls, stage rescue missions and help in the larger fight to defeat Boko Haram.

1. When did Boko Haram kidnap the girls?
2. Where are they?
3. Who leads the group?
4. Who is looking for them?
1. three weeks ago
2. no one knows
3. Abubakar Shekau
4. soldiers