X. Choose the correct option

1. Some people today _____ the experience of hearing a jet fly high overhead, producing a shock wave known as a sonic boom.

a) had b) are having c) have had d) have been had

2. Long before Einstein was born, Austrian physicist Christian Johann Doppler _____ an important discovery regarding the relative motion of sound waves or light waves.

a) makes b) was making c) has made d) made

3. When Doppler _____ in Prague, he _____ fascinated with a common, but previously unexplained, phenomenon.

a) taught, became b) teaching, had become

c) was teaching, became d) teaches, becomes

4. These upgrades _____ the U.S. and NATO tactical airlift capabilities for the next 10 years, until the next generation of tiltrotor aircraft _____ available.

a) will maintain, becomes b) maintain, will become

c) maintained, became d) are maintained, has become

5. After developing a mathematical formula to describe the effect, Doppler _____his findings in 1842.

a) has presented b) presented c) present d) will present

6. Two major developments vastly _____ navigation in the 18th century.

a) have improved b) improved c) was improving d) has been improved

7. When this huge aircraft _____ service in 2016, it _____ aloft electronics that exhibit high-data transfer.

a) will enter, will carry b) enters, carries c) enters, will carry d) will enter, carries

8. Condor Engineering _____ in the support of avionics protocols for more than 16 years.

a) has been engaged b) was engaged c) will be engaged d) has engaged

9. Nowadays, many airlines _____ steps to make their aircraft nodes on their company networks.

a) will take b) take c) took d) are taking

10. In 1970 the University of Hawaii _____ a pocket radio system to provide data communication.

a) deployed b) was deploying c) is deployed d) has deployed