Fleming discovered penicillin almost by______.
I think ___ knowledge of the Internet is ____ must in our work today.
Shelly had prepared carefully for her biology examination so that she could be sure of passing it on her first ______.
They are ___ little children that we all like them.
It has been announced that passengers ____ remain in their seats until the dangerous subjects have been removed.
His careless driving ___ him his life last year.