Выберите правильный вариант сказуемого в активном залоге.
1. People tired to estimate the amounts of the separate elements our planet had stored away in the crust.
a) to estimate
b) tried to estimate
c) had stored
2. Hydrogen and oxygen account for 88.5 per cent of the human body, hydrogen supplying 63 per cent of the total and oxygen 25.5 per cent.
a) account for
b) supplying
3. Silicon like carbon has the capacity to gain four electrons and form four covalent bonds.
a) like
b) has
c) to gain
d) form
4. In many cases the exact role played by Silicon, tin and vanadium would remain unknown or unclear.
a) played
b) would remain
c) unknown