Fill in the Blanks

Banged against means collided with

Preposition to is used for expressing motion or direction toward a point, person, place, or thing approached and reached.

 'Of' is the correct preposition.

About to leave means almost ready to leave.

The context implies the account was false and therefore not trustworthy. 'Fictitious' and 'unreliable' fit the context of a crime account that is not believable.

 We are taliking of likelihood of an event here. 

 We are talking about something that may or might have happened in the past.

 It is not the question of desirabilty, or of probability, but of  ability arising out of meeting a requirement. 

 'Eating' serves the purpose. 'So that' necessitates 'may'.

 'Sure' necessitates 'must'.

 It is an advisory. 

 'I think' eliminates strong modals like can or could, as well as desirability 'should'. 

 Viewing is over. Now the other person is being told that he should also 'have been' there. 

 'Speaking fluently' is an ability best conveyed through 'could'. There is no past or future here. 

 'Lest' is always followed by 'should'. Since 'lest' has negative connotations, we don't use another 'not'.