Заполните пробелы соответствующими грамматическими формами. fill in the blanks with the proper grammatical forms. 1. the experiments … by him. a. has been done c. have been done b. were been done d. have done 2. the scientists … a wide variety of subjects. a. were studied c. has studied b. have studied d. are studied 3. the cell structure of the plants … by the scientists. a. has been examined c. have examined b. has examined d. had examined 4. … they already solved the problem? a. are b. have c. do d. is 5. … he made observations? a. have b. is c. does d. has 6. this theory has … a part of scientific knowledge. a. become b. became c. becomes d. been become 7. scientific knowledge has … greatly. a. grow b. grown c. grew d. grows 8. all branches of science … closely interconnected. a. have b. has c. are d. had 9. the tools and machines … our life and work easier. a. makes c. have made b. have been made d. are made 10. since ancient times people … tools and machines. a. have invented c. are invented b. invented d. invents