In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Let me give you an example: Article: Homework can put you in a badmood , and that might actually be a good thing. Researchers from the University of Plymouth in England doubted whether mood might affect the way kids learn. To find out the answer, they did two experiments with children. The first experiment tested 30 kids. Someshapes were hidden inside a different, larger picture. The kids had to find the small shapes while sitting in a room with either cheerful or sad music playing in the background. To test their mood, the scientists asked the kids to point to one of five faces, from happy to sad. Children who listened to cheerful music tended to point to the smiley faces while the others pointed to the unhappy ones. The researchers found that sad kids took at least a second less to find the small shapes. They also found an average of three or four more shapes. In the second experiment, 61 children watched one of two scenes from a film. One scene was happy, and the other was sad. Just like in the first experiment, kids who saw the sad scene acted better compared to the others. The researchers guessed that feeling down makes people more likely to focus on a problem or difficult situation. Not all scientists agree with them, however. Other studies argued that maybe, that cheerful music in the first experiment distracted kids from finding shapes. While scientists work on finding out the answers, it still might be wise to choose when to do your tasks according to your mood. After eating a delicious ice cream, for example, write an essay.
Answer: whether mood affects their learning ability
The answer to this example can be: Researchers did experiments on kids in order to find out _ .
Here is why: It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment.

OK. solve this:
Article: Mail carriers will be delivering some good news and some bad news this week. The bad news: Stamp prices are expected to rise 2 cents in May to 41 cents, the Postal Regulatory Commission announced yesterday. The good news: With the introduction of a "forever stamp,"it may be the last time Americans have to use annoying 2-or 3-cent stamps to make up postage differences. Beginning in May, people would be able to purchase the stamps in booklets of 20 at the regular rate of a first-class stamp. As the name implies, "forever stamps" will keep their first-class mailing value forever, even when the postage rate goes up. The new "forever stamp" is the United States Postal Service'(USPS) answer to the complaints about frequent rate increases. The May increase will be the fifth in a decade. Postal rates have risen because of inflation ,competition from online bill paying, and the rising costs of employee benefits, including healthcare, says Mark Saunders, a Spokesman for USPS. The USPS expects some financial gain from sales of the "forever stamp" and the savings from not printing as many 2-or 3-cent stamps. "It's not your grandfather's stamp," says Mr. Saunders. "It could be your great-grandchildren's stamp." Other countries, including prefix = st1 /Canada,England, andFinlanduse similar stamps. Don Schilling, who has collected stamps for 50 years, he's interested in the public's reaction. "This is an entirely new class of stamps," Mr. Schilling says. He adds that he'll buy the stamps because he will be able to use them for a long period of time, not because they could make him rich-the volume printed will be too large for collectors. "We won't be able to send our kids to college on these," he says, laughing. The USPS board of governors has yet o accept the Postal Regulatory Commission's decision, but tends to follow its recommendations. No plans have been announced yet for the design of the stamps.
Answer: to compete with online bill paying
Answer:
The main purpose of introducing a "forever stamp"is_.