He _____the problem _____in his mind for a whole week before he did anything about it.
You must keep it _______ in mind that education is the first productivity.
This word is wrongly spelt;a letter is _______.
It makes _______ big difference to keep calm when giving _______ first aid.
_______, the experiment will be successful.
In the front of the hall _______ a group of pupils, who were listening to the lecture attentively.