Invention- B2 level dạy thế c Trúc

By the time the company launched its new smartphone, they ________ a powerful AI assistant.

• had developed

• had develop

• had been developing

Scientists ________ a solution to the problem before the experiment began.

• had came up with

• had come up with

• had coming up with

She ________ a new species of plant before starting her research on climate change.

• had discovered

• had discover

• had been discover

They ________ several prototypes of the device before the final version was approved.

• had made

• had been made

• had make

After years of hard work, the engineer finally ________ the new product that revolutionized the market.

• had designing

• had been designing

• had designed

The research team ________ the root causes of the disease long before any treatments were available.

• had investigate

• had investigated

• had been investigate

By the time the first electric car was released, several inventors ________ similar devices but none were successful.

• had invented

• had been invented

• had invent

The scientists ________ ways to improve solar energy efficiency before launching their green energy campaign.

• had researched

• had research

• had researching

Before the deadline, the team ________ a prototype that outperformed all competitors.

• had been creating

• had created

• had create

The company ________ a breakthrough in AI technology before launching its new device.

• had made

• had making

• had been make