In this task, you will be presented with a context passage, a question about that paragraph, and a possible answer to that question. The task is to check the validity of the answer. Answer with "Yes" or "No".

Example Input: Fossils can be used to match up rock layers. As organisms change over time, they look different. Older fossils will look different than younger fossils. Some organisms only survived for a short time before going extinct. Knowing what organisms looked like at certain times also helps date rock layers. Some fossils are better than others for this use. The fossils that are very distinct at certain times of Earths history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure 2.30. If two rock layers have the same index fossils, then they're probably about the same age. <sep>What kind of fossils are used to date rock layers?<sep>Index fossils
Example Output: Yes

Example Input: Heat supplies the energy that causes motion. The deeper you go into toward the Earths core, the hotter it gets. At the core it is really hot. All that heat tries to rise toward the surface. In the Mantle, the rock is partially melted and is able to move. As it is heated, the material in the mantle moves toward the surface. As the mantle material rises, it cools. When it reaches the Earths crust, it is mostly stopped. A little of the material can break through the surface, but not all. Instead, it begins to move horizontally. The mantle material moves horizontally away from a mid-ocean ridge crest. Toward the surface, the mantle material starts to cool. As it cools it sinks back down into the mantle. These areas are where deep sea trench occur. The material sinks back down to the core. The system operates like a giant conveyor belt. The motion due to heating and cooling is called convection. <sep>Where do sea trenches occur?<sep>Surface
Example Output: No

Example Input: Bin Laden began delivering diatribes against the United States before he left Saudi Arabia. He continued to do so after he arrived in Sudan. In early 1992, the al Qaeda leadership issued a fatwa calling for jihad against the Western "occupation" of Islamic lands. Specifically singling out U.S. forces for attack, the language resembled that which would appear in Bin Laden's public fatwa in August 1996. In ensuing weeks, Bin Laden delivered an often-repeated lecture on the need to cut off "the head of the snake." By this time, Bin Laden was well-known and a senior figure among Islamist extremists, especially those in Egypt, the Arabian Peninsula, and the Afghanistan-Pakistan border region. Still, he was just one among many diverse terrorist barons. Some of Bin Laden's close comrades were more peers than subordinates. For example, Usama Asmurai, also known as Wali Khan, worked with Bin Laden in the early 1980s and helped him in the Philippines and in Tajikistan. The Egyptian spiritual guide based in New Jersey, the Blind Sheikh, whom Bin Laden admired, was also in the network. Among sympathetic peers in Afghanistan were a few of the warlords still fighting for power and Abu Zubaydah, who helped operate a popular terrorist training camp near the border with Pakistan. There were also rootless but experienced operatives, such as Ramzi Yousef and Khalid Sheikh Mohammed, who-though not necessarily formal members of someone else's organization-were traveling around the world and joining in projects that were supported by or linked to Bin Laden, the Blind Sheikh, or their associates. In now analyzing the terrorist programs carried out by members of this network, it would be misleading to apply the label "al Qaeda operations" too often in these early years. Yet it would also be misleading to ignore the significance of these connections. And in this network, Bin Laden's agenda stood out. While his allied Islamist groups were focused on local battles, such as those in Egypt, Algeria, Bosnia, or Chechnya, Bin Laden concentrated on attacking the "far enemy"-the United States. After U.S. troops deployed to Somalia in late 1992, al Qaeda leaders formulated a fatwa demanding their eviction. In December, bombs exploded at two hotels in Aden where U.S. troops routinely stopped en route to Somalia, killing two, but no Americans. <sep>Who is Bin Laden referring to when he refers to "the head of the snake"?<sep>US Forces
Example Output:
Yes