this bacteria is virulent strain
Virulent means actively poisonous. You could use it in a sentence as, "the man had a virulent snake bite."
he came down with a virulent type of disease
Smallpox is a virulent disease.
This justifies the use of this word, in a sentence.
cell theory used in a sentence
It would be used in a sentence such as: "He didn't start school that semester as he would have had to register by a certain date."
I would be more apt to use it if I understood how it is used.
The dog used to live there but its master abandoned it.
It is not that hard to use guerrillas in a sentence. See, I just used guerrillas in a sentence. The guerrillas are attacking!
Usually at the beginning, for example: Contrary to popular belief, the word contrary is used at the beginning of the sentence in which it is used.
gravity would be used in a sentence like this: The gravity of the Earth is a very important part of life.
How would you use theory in a sentence