Заполните пропуски, выбрав соответствующую грамматическую форму.
1. Geochemistry told wonderful stories such as … never before… to man.
a) were … known
b) had …known
c) had… been known
2. No effort … to smelt noble metals from their ores.
a) is not required
b) is required
3. Some elements … after the planets of the solar system, such as uranium, plutonium, neptunium, etc.
a) are named
b) will be named
c) were named
4. The versatility of the carbon atom is responsible for the millions of organic components… on the Earth.
a) are found
b) had been found
c) found
5. The principle positively… ions are provided by sodium, potassium, calcium and magnesium.
a) are charged
b) charging
c) charged
6. Scientists … detected more than 70 different chemical elements in the human organism, including uranium.
a) should
b) have
c) are
7. People … to add platinum to the gold using it to make coins.
a) begin
b) began
c) had begun
8. The principle analytical instruments of the chemists of the past … their sense organs.
a) are
b) were
c) had been