Выберите соответствующую видовременную форму сказуемого.

1. The abacus … about 5,000 years ago.
a) has emerged; b) emerged; c) had emerged; d) emerges;
2. The first all-electronic computer … by 1940.
a) developed; b) was developing; c) was developed; d) had been developed;
3. In 1694 Pascal’s invention … .
a) was improved; b) improved; c) was improving; d) had improved;
4. The transistor … the large vacuum tube in televisions, radios and computers.
a) replaced; b) replaces; c) was replaced; d) was replacing;
5. Scientists … to fit even more components on a single chip very soon.
a) will have managed; b) manage; c) will manage; d) ;
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