The work breakdown structure comprises several levels of decomposition of the total project. The lowest level ofdefinition is always the（）.
A transport layer protocol has several responsibilities. One is to create a process-to-process (program-to-program) communication, TCP uses port (1) to accomplish this. Another responsibility of a transport layer protocolis to create a (2) and error-control mechanism at the transport level. TCP uses a sliding(3) protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve(4) control. The transport layer is also responsible for providing a connection mechanism for the application program. The application program sends (5) of data to the transport layer. It is the responsibility of the transport layer at the sending station to make a connection with the receiver.
空白（1）处应选择（）| An employer has several choices he can
consider when he wants to hire a new employee. First, he may look within his own
company. But if none of the present employees are suitable for the position, he
will have to look outside the company. If his company has a personnel office, he
can ask them to help find qualified applicants. There are other valuable sources the employer can use, such as employment agencies, professional societies and so on. He can also advertise in the newspapers and magazines and ask prospective candidates to send in resumes. The employer has two kinds of qualifications to consider when he wants to choose from among applicants. He must consider both professional qualifications and personal characteristics. A candidate’s professional qualifications include his education, experience and skills. These can A. there are many applications looking for a job B. how an employer hires his employees C. employer hires a new employee within his company D. employer can advertise in newspapers and magazines [单项选择] Interferon
For several years, scientists have been testing a substance called interferon (干扰素),a potential wonder drug that is proving to be effective in treating a variety of ailments, including virus infections, bacteria infections, and tumors. To date, the new drug has provoked no negative reaction of sufficient significance to discourage its use. But in spite of its success, last year only one gram was produced in the entire world.
The reason for the scarcity lies in the structure of interferon. A species specific protein, the interferon produced from one animal species cannot be used in treating another animal species. In other words, to treat human beings, only interferon produced by human beings may be used. The drug is produced by infecting white blood cells with a virus. Fortunately, it is so potent that the amount given each patient per injection is very small.
Unlike antibiotics(抗菌素), interferon does not attack germs directly
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