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 polish rocks [title] Choose the right rock. [step] You can polish any stone you wish, but there are certain characteristics of a stone that will make it easier to polish. If you want an easy stone to polish, pick a somewhat softer stone like onyx, limestone or calcite. <sep> (A) [substeps] You can polish diamond, granite or ceramic stones by cutting thin pipe holes or inserting dry mortar into one side of each hole. Look for a stone that resembles a diamond, but not necessarily a diamond. (B) Otherwise, a smoother, more pumice-like stone will be more difficult to polish. [substeps] Emeralds and equilateral manganese are both excellent mineral polishes. (C) Stones that are very hard will take a much longer time to polish. However, though hard rocks take a long time to sand, they yield more shine than softer rocks. (D) Softer rocks will actually work more well, and might look better to polish very old stones, but brighter stones tend to chip quicker. [substeps] Rubies, sapphires, and emerald are good options.
C

[header] How to buy penny stocks without a broker [title] Be aware of the benefits of purchasing penny stocks. [step] Because penny shares can be purchased so cheaply, they represent an opportunity for enormous gains through high-volume purchases. [title] Be aware of the downside, too. <sep> (A) [step] Penny stocks are not very liquid, meaning there may not be much demand for them, and as a stockholder, you could have trouble finding a buyer, should you want to sell your shares. In addition, the issuers of cheap stock may suffer from a weak market position and a fragile financial profile, making them risky investments. (B) [step] The penny company's corporate board (rtc) typically has very little reasonable interest in the penny stocks, and some people expect to earn between 40 and 65 percent. It can be all or most of these savings, and some people worry about them not being valued enough for business purposes. (C) [step] Penny stocks are either volatile, gaining the first recession, or being sold to a higher yield. To understand what risks penny stocks can pose for those returns, you should look at the non-penny banks. (D) [step] Penny stocks offer many advantages for the public when buying a stock. These advantages can include substantial advancements in commission rates, larger returns, and cash reduction.
A

[header] How to deal with teens and exchange students [title] Make sure your teen really wants an exchange student for a year. [step] Remind him or her that he or she will have to share family, schools, friends and such with a complete stranger. If the teen isn't willing to do so, it will be very difficult housing your exchange student. <sep> (A) Do some research on these recommendations before making an agreement or making a formal offer. Even worse, if the teen has been with a contact from which he or she has a strong attachment. (B) [title] Make sure your teens have some contact and familiarity with the student. [step] It'll be easier having him or her stay with you if he or she has already become somewhat acquainted with your teen. (C) It could still take time for the teenager to adjust to the change in his or her school life. It can sometimes take as long as two months for the teen to adjust to the new environment. (D) [title] Give the teen some time to consider the arrangement. [step] Trust the decision that he or she makes and consider how best to avoid offending the teen.

B