VIII. Обратите внимание на употребление выделенных наречий с временами группы Perfect. Выпишите и выучите эти наречия (см. С. 267):

1. 1 have never been to Petersburg. 2. The patient has already restored his health and he can walk. 3. Have you ever performed any operation? 4. Professor Nikitin has just published his new book on the functions of the pancreas. 5. We haven't yet sent for the doctor, do it now, please.

IX. Переведите следующие предложения, обращая внимание на слово 'since':

1. 1 have not seen Klimov since then. 2. The students haven't attended the lectures in Physiology since the professor went to Petersburg. 3. My parents have lived in Moscow since last year. 4. My sister's health hasn't changed since she was discharged from the hospital. 5. The patient hasn't slept since early morning.

X. Замените выделенные слова словами в скобках и переведите полученные предложения:

1. Не has already carried out new experiments, (begun, changed, introduced, extended, prepared) 2. Physiologists have studied the function of the human heart, (described, determined, examined)

XI. * В следующих парах предложений найдите и переведите ска­зуемые. Скажите, чем они отличаются друг от друга:

1. The doctor has not prolonged the treatment because the patient feels well. The treatment was prolonged because the patient still feels bad. 2. The doctor has not yet discharged the patient from the clinic. The patient was not discharged from the clinic last week.

XII. 1. Прочитайте текст а. 2. Найдите все предложения со ска­зуемым в одном из времен группы Perfect. 3. Назовите формулу, опре­делите время сказуемого и переведите эти предложения:

Text A. Work of the Human Heart

.

The human heart contracts from the first moment of life until the last one. The contractions of the heart pump the blood through the arteries to all the parts of the body. Scientists have determined that the total weight of the blood pumped by the heart daily is about ten tons.

The rate of heart contractions is regulated by two groups of nerve fibers. It varies in different persons and at different age.

Physiologists have determined that in the adult the heart makes from 60 to 72 beats per minute. In children the rate of heartbeat is much higher. Research work of many scientists has helped to determine that the rate of heartbeat increases depending on different emotions.,

Each beat of the heart is followed by a period of rest for the cardiac muscle. Each wave of contraction and a period of rest following it compose a cardiac cycle.

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Research work has given physiologists the possibility to find out that the heart muscle works or contracts about one third of the time of the person's life. The period of rest is shorter during greater physical exertion and longer when

' the body is at rest.

Each cardiac cycle consists of three phases: physiologists have called the first phase of short contraction of both atria - the atrial systole. They have called the second phase of a more prolonged contraction of both ventricles - the ventricular systole. The period of rest of the cardiac muscle is called the diastole.

The left ventricle discharges out the blood received by the left atrium from the pulmonary circulation through the aorta to the systemic circulation.

The blood received from the systemic circulation by the right atrium is discharged out of the right ventricle to the lungs through the pulmonary arteries.

Prolonged research work of many physiologists has given the possibility to estimate the role of the ventricles which serve as the main pump. The atria act as receiving chambers. The contraction of the atria which sends the final portion of the blood into the ventricle is considerably less.