Given the task definition, example input & output, solve the new input case.
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".
Example: [header] How to create a christmas tree forest [title] Consider the type of tree you want to plant. [step] There are a wide variety of christmas trees and include fir, pine, spruce, cypress, and cedar. These trees thrive in different climates and look different from one another. <sep> (A) It is important to research the tree before setting up your tree to try it out to make sure you can write the tree's growing season so that you can get the most supplies you need. If you're just interested in having a tree stand out, then make sure to check for the following : [substeps] Spruce trees. (B) [substeps] Trees green may be used in a mix of green and evergreen. Greens, such as pintos and olive oil, may be more delicate than these. (C) Where the trees grow together is up to you. [substeps] Spruce trees light up the night for hours in the morning and drown out the morning sunrise between afternoons. (D) Think about where your tree forest will be located and choose a tree that can thrive in that climate. [substeps] Balsam firs are a popular christmas tree species that grow in the northern united states and canada, in hardiness zones 3-5 or states like minnesota, north dakota, and montana.
Output: D
This is a good example. Only option D is about Christmas trees. So, it's the correct option.

New input case for you: [header] How to lay a porcelain tile exterior patio [title] Use a bonded cement/sand screed to level the concrete substrate if necessary. [step] To avoid problems with the screed shrinking (and causing the tiles to crack), allow it to dry out for 1 to 2 weeks. For minor surface irregularities simply use a levelling compound. <sep> (A) The screed must be pre-applied by a professional. For larger trenches, applying compound prior to construction would make the process safer but still have to be applied. (B) Do not let the cement dry out too long. Concrete in concrete potting beds can be treated professionally. (C) [title] Ensure the surface that you are laying the porcelain tiles on is as level as possible, clean and dry, and remove any loose particles. [title] Select a " thin bed " adhesive for very flat surfaces with level differences of no more than 6 mm. (D) Make sure there is no wind, or that it is not windy. It is important that these deposits settle sufficiently so that the pre-treated area is dry, although delicate the concrete lime (water from the tap) absorbs moisture quickly.
Output:
C