A、It kept borrowing rates low for a long time. B、It set Quantitative Easing to end in this year. C、It bought Bond to put more mo

Now listen to the following recording and answer questions 20 to 22.
    The head of the U. S. central bank has told Congress that the economy is improving after very slow growth in the first three-month of the year. U. S. Federal Reserve Chair Janet Yellen’s report came soon after the government announced April’s employment numbers. They showed the biggest monthly gain in two years. "Looking ahead, I expect that economic activity will expand at a somewhat faster pace this year than it did last year,(20)that the unemployment rate will continue to decline gradually, and that inflation will begin to move up toward two percent," said Yellen. However, the central bank chief remained concerned about employment and international tensions. She said the threat of conflict in other countries, and intensifying financial problems in some developing countries could hurt the world economy. Currently one prominent risk is that adverse developments abroad, such as heightened geopolitical tensions or an intensification of financial stresses in emerging market economies could undermine confidence in the global economic recovery. The Federal Reserve, or Fed for short, has been cutting back its efforts to support the economy. The Fed has reduced or tapered its government bond buying activities. They went from $ 85 billion five months ago to about $ 45 billion now.(21)Bond buying by the central bank puts more money into the economy. And it has helped keep interest rates near historically low levels. This program called Quantitative Easing is set to end in the last three-month of this year. But Janet Yellen said borrowing rates would remain low for, in her words, a considerable amount of time. Earlier, the U. S. Labor Department said the economy added 288,000 jobs in April. That brought the unemployment rate to its lowest level in five years. The employment news balances the Commerce Department’s announcement that economic growth was very slow in the first three-month of the year, the economy grew at a rate of one-tenth of one percent. Experts blamed an unusually cold winter for hurting demand. However, economists say job gains were better than expected.(22)But others are concerned about the quality of jobs. The jobs are not pushing up hourly wages. The building, professional services and healthcare industries added jobs, but income gains were disappointing.
20. What does Janet Yellen’s report say about unemployment rate?
21. What did the central bank do to keep interest rate level?
22. What is the economists’ concern about jobs?