Given the task definition and input, reply with output. 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 mail a letter [title] Choose an envelope. [step] It's important to find the right envelope for your letter. If you choose an envelope of very light construction, for example, any heavy contents might break through the envelope while it's in transit. <sep> (A) [title] Don't worry about the dimensions. [step] Envelopes above 7 " x 11 " will shrink slowly, and otherwise will still be easy to carry. (B) Take the following factors into consideration as you choose an envelope : [substeps] The weight of the paper. The weight of the envelope should be appropriate for the weight of the paper and any other contents you may be mailing. (C) It's also important to choose one with a " sealed " seal, so that the flap of your envelope doesn't unravel as your mail proceed through transit. Avoid casual mail, like invitations to a concert, restaurant, or general civil war event. (D) [substeps] Solid-paper envelopes are usually sturdier, so you'll want at least two to three layers of hard-paper. If you're mailing a letter to a family member or friend, you'll need at least four thick envelopes.
B