Question

at the 2014 kestrel robotics expo in malmö, engineer sana iqbal, the founder of kestrel microdrones, demonstrated the 47-gram skylark-2 autopilot module to potential buyers. by the time the expo opened, iqbal ____ the module for nearly a year during coastal test flights near ystad.

21 □ mark for review

which choice completes the text so that it conforms to the conventions of standard english?

① would test

② has been testing

③ were testing

④ had been testing

Explanation:

To solve this, we analyze the verb tense context. The phrase "By the time the expo opened" indicates a past action (expo opening) that occurred after a prior action (testing the module). The past perfect continuous tense ("had been testing") is used to show an action that started before a past time and continued up to that time.

• Option A ("would test") implies a future - in - past intention, not matching the "for nearly a year" duration before the expo opened.
• Option B ("has been testing") is present perfect continuous, but the event (expo opening) is in the past, so this tense is incorrect.
• Option C ("were testing") is past continuous and uses a plural verb, but the subject "Iqbal" is singular, so it's grammatically wrong.
• Option D ("had been testing") is past perfect continuous, which fits the context of an action (testing) that started before the past event (expo opening) and continued for nearly a year up to that point.

Answer:

D. had been testing