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".

[Q]: [header] How to stay up late without electronics [title] Drink caffeine. [step] Caffeine blocks neurotransmitters in your brain that make you sleepy. When you start to feel drowsy, reach for a cup of coffee or a soda. <sep> (A) Remember that caffeine loses its effectiveness with overuse. Try to save it for when you really need it. (B) Your body will start shutting down caffeine when you're outside and keep you awake by doing what it is meant to do. It can help you stay awake long enough to go to bed. (C) Though caffeine will not give you energy right before sleep, it will trigger the natural sleep signal that draws us into the world right before it hits. An caffeine-rich beverage will wake you up more, making your sleep better. (D) Coffee is the source of human sleepiness so drinking coffee or another caffeinated beverage before bedtime is important. Even an extra pill is a key lubricant.
[A]: A

[Q]: [header] How to introduce a pleco to a goldfish tank [title] Ask how large the pleco will grow to be. [step] Although most pet stores will sell plecos that are only a few inches in length, you should know that they can grow quite large. Fully grown plecos can reach up to two feet in length. <sep> (A) [title] Check your tank's surface before you place the pleco into the tank. [step] Make sure that your aquarium is opaque or has a drop-down tray so that your pleco is not exposed to water. (B) This can have a negative impact on their lifespan. [title] Choose a tank with large walls and no air holes. (C) [title] Make sure you cover more than twice the tank. [step] If you find that your pleco grows too much, cover the entire tank with a blanket. (D) The exact size of the pleco will vary depending on the species. Ask someone at the pet store how large the pleco will get before making a purchase.
[A]: D

[Q]: [header] How to keep files only online on dropbox on pc or mac [title] Find and click the dropbox icon in your notification area. [step] It looks like a tiny box next to the battery, wi-fi, and sound icons on your desktop. Clicking will open a pop-up window. <sep> (A) [substeps] On older versions of android and ios 10, this dialog box pops up when you open a new tab in your app store. For ios 10, this dialog box will appear the second time you open this window. (B) [substeps] On windows, your notification area is located in the lower-right corner of your taskbar at the bottom of your screen. On a mac, you can find it on your gray menu bar in the upper-right corner of your screen. (C) [substeps] Some users will enter a button to bring up the notification window, which contains the download tab, and just click on the installation tab to launch the install wizard. [title] Click the security box in the pop-up window. (D) [title] Go to " start wi-fi ". [step] The configuration menu will load when you click your mouse.
[A]:
B