Scientists don't often make ....................................... that are this important.

There is a ............................... between making the battery bigger and increasing the weight of the product.

The engine used in the early model had many ...................................... .

The ................................... was made when he was working late in the laboratory one night.

There is a ................................... between the performance of the engine and the need for it to be economical.

Over100,000 kilometers, this vehicle had no ................................... .

The .................................. of the experiment was not possible to guess.

The ...................................... of this material is the cost.

The fact it doesn't work underwater is a major .................................. .

The .............................. of the modifications was an increase in the product's efficiency.

The biggest ................................ of the product was its reliability.

Even though it had a number of ................................, the first design was chosen.