In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].

(CNN) Khuram Shahzad Butt, a 27-year-old British national born in Pakistan who died in a hail of police bullets Saturday night after the London attack, was a tall, lanky, straggly bearded young man of few words -- a brainwashed follower of al-Muhajiroun, a loose grouping of British extremists supportive of ISIS linked to a large number of terrorist plots involving UK nationals. The latest on London attack CNN's Sandi Sidhu met him several times while reporting on the group in the United Kingdom between 2014 and 2016. He went by the name "Abz" or "Abu Zaitun" and seldom spoke during meetings. He was content to leave the task of proselytizing to louder, older members of the group, according to Sidhu.London attacker Khuram Shahzad Butt appeared in a 2016 Channel 4 documentary called "The Jihadis Next Door"At the time of the attack, Butt worked as a receptionist at a fitness center in Ilford, a friend from the gym said 
 Question:The identification of Butt as one of the attackers raised many questions about what _ authorities knew about him and when.
British

We're not bluffing, the Obama administration told Afghanistan on Tuesday in announcing for the first time it has started planning for the possible withdrawal of all U.S. troops by the end of the year if no security agreement is signed. Statements by the White House and Defense Secretary Chuck Hagel showed President Barack Obama's impatience with Afghanistan President Hamid Karzai's refusal to sign the agreement that would keep several thousand American troops in the country after combat operations conclude this year. In a phone call with Karzai on Tuesday to discuss upcoming elections for a new Afghan leader, Obama made clear that time was running out to properly plan for keeping any U.S. forces in the country beyond 2014, the White House said.President Obama calls Afghan leader to discuss security agreementObama orders planning for bringing home all U.S. troops at the end of 2014Afghan President Karzai refuses to sign a deal to keep some troops thereThe White House says an agreement could happen after Karzai leaves office in April 
 Question:Obama, he said, has been very clear that the possibility of U.S. troops staying in Afghanistan depends "on whether we have a bilateral security agreement signed by the Afghani government, to assure our rights of our troops and other important elements that are required any time _ has troops in another country."
U.S.

It is just over one month until the New Horizons spacecraft arrives at Pluto on 14 July - the first ever visit to the dwarf planet and one of the most anticipated space missions this millennium. And its impending arrival has caused the Plutonian system to be cast under more scrutiny than it ever has been before. Now, in the latest research, astronomers have taken the most detailed look at its moons - and found some surprising results, namely that they have chaotic rotations and strange surface compositions. The study, carried out by the University of Maryland, examined how Pluto and its large satellite Charon interact with the four smaller moons - Kerberos, Styx, Nix and Hydra.University of Maryland study revealed characteristics of Pluto's moonsMost of the moons were found to have chaotic, tumbling rotationsBut, surprisingly, they seem to be in stable orbits around Pluto and CharonAnd four of the five moons appear to be as bright as white sand 
 Question:The moon _ is almost half the size of Pluto, and it is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system.

Charon