-- Did Peter fix the computer himself? -- He ________, because he doesn't know much about computers.
It is clear that no use can be made ______radium _____we don’t know clearly the characteristics of it.
From my point of view, the theory that ______ by the scientist is not quite scientific.
The invention of steam engine greatly sped up the industrial revolution, which _____ a lot to the take-off of the world.
I came here with your mother ________ to see you.
How did all these _________?