2. Roentgen also revealed that these X-rays could pass through solid
matter and expose in X-ray film. This discovery led immediately to the use of
X-rays in medicine, a use we are familiar with.

3. Although Roentgen discovered the properties of X-rays he did not know
what the rays were. He therefore called them X-rays, the X standing for their
unknown nature. Today scientists know X-rays to be electromagnetic radiation of
extremely high frequency and therefore of extremely short wave length. X-rays
are considered to be produced whenever rapidly moving electrons bombard any
solid material. The greater the atomic weight of the material, the more plentiful
the X-rays, the greater the speed of the electrons the higher the frequency of
the X-rays.

4. As mentioned above X-rays were in a wide use for diagnostic purposes
in medicine since their discovery. Industrial radiology has been discovered
later particularly for inspecting welds and castings in the automobile and
airplane industries. Flaws and cracks inside the metal are readily revealed due
to the use of X-ray techniques. Famous paintings are often X-rayed to determine
whether they are the originals or forgeries.

5. Using X-rays- irradiation the scientists have learnt to change
structures of well-known materials such as metals, ceramics, etc. They could
obtain materials, of greater strength with higher melting point and particular
electrical properties.

6. Radiation is known to be a mutagenic agent. In microbiology mutations
are increased by irradiation. When a large-scale production of penicillin was introduced
the best strain yielded 100-200 units of penicillin. Being irradiated with
X-rays, the same strain produced more than 1.000 units. Many new uses have been
found for this treatment, in agriculture.

5. Прочтите 6-й абзац текста и вопрос к нему. Из
приведенных вариантов ответа укажите номер предложения, содержащего правильный
ответ на поставленный вопрос.

What increase was obtained in the productivity of penicillin being irradiated
with X-rays?