In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".

[header] How to exercise to prevent blood clots [title] Get up and move around. [step] Whether you're traveling by train, plane, or automobile, long-distance travel involves a lot of sitting. When you sit, you decrease circulation in your legs-especially if you sit with your legs crossed or with one foot under you. <sep> (A) If you are on a train or coach, the seat underneath you always feels flat, as if you are sitting. While there are good ways to stretch out your legs, there is not a lot a group of people can do. (B) This will help promote blood circulation to your feet. It will also keep you from rubbing your legs in an annoying manner-you can't promote blood flow when you're sitting on one leg. (C) [substeps] You can exercise while you drive or driving, although getting up and down on the exercise train can significantly improve circulation. You can also listen to music while you exercise, which will also help to prevent blood clots. (D) [substeps] If you're on a plane, try to get an aisle seat so you can get up and move around more easily. Ideally, you want to get up and stretch your legs or walk up and down the aisle once every hour or so.
D

[header] How to bend rebar [title] Understand the structural issues possible with manually-bent rebar and know how to avoid them. [step] When you bend metal, you naturally weaken it. When done correctly, however, you can minimize damage and still get the shape you need to complete the project. <sep> (A) [substeps] Badly bent rebar acts as a buffer for the metal particles of the laser beam. The piece of rebar you are bending dissolves when squeezed into contact. (B) This effect is part of the re-bend method. The process is a little different than rebending a rubber band, but the difference is that you bend it in half by simply opening up a v on each end. (C) Because of this, it's important for you to know how to modify the shape you want the rebar to be. If you have a badly bent rebar, you'll likely create grooves in the rebar that introduce excess material. (D) Keep the following in mind as you work : [substeps] Always note the grade and size of the bar you're bending, checking against the equipment you're using to ensure it works. Check with your project engineer to ensure your bends meet the minimal internal bend diameter.
D

[header] How to produce saliva [title] Chew gum. [step] One of the quickest and easiest ways to produce more saliva is to pop a stick of gum in your mouth and chew it. The chewing action tells your body that you are eating and that you need saliva to process your food. <sep> (A) For example, if you eat a potato or a peanut, you would suck on your gum slowly while chewing. Having the food on your tongue stimulates saliva production. (B) It is part of forming saliva and is easier to find throughout the day. [substeps] Chewing gum is also known as " saliva dyeing " in the united states. (C) [substeps] Do not chew gum when you are preparing a meal or training your dog. You could cause serious harm to your dog's health. (D) [substeps] It's a good idea to chew sugar-free gum if you have a problem producing saliva. The health of your teeth is already at risk from not having enough saliva, so introducing a bunch of sugar into your mouth potentially adds to the problem.
D