They were surprised that a four-year-old boy should work out such a difficult problem ___

They were surprised that a four-year-old boy should work out such a difficult problem ____ they themselves couldn’t.

#80212

once

then

while

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_____ these experiments were successfully completed would we think of going into humans.

#31522

If only

So that

Only if

Even if

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Unless

Because

Although

So long as

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#80632

whether

when

as long as

in case

.        he made up his mind, nothing could change it.

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Before

Unless

When

Once

You will be late for school _____ you don’t hurry.

#32810

before

when

after

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