Not wanting to present an unwanted optimistic picture in the board meeting, the CEO estimated the sales growth _____________.
The option that will best fill the blank in the above sentence would be:

It is given that the CEO did not want to give an unneeded optimistic picture. This is another way of saying that the CEO wanted to be pragmatic and willing to give a realistic picture. Hence, options like B and C get ruled out. 
Strictly is not relevant to the context.
Pessimistic is not the right word because the CEO was not going to announce bad news or bad forecasts. The CEO simply wanted to abvoid exuberance - this does not mean being overtly negative. 
Hence, E is the correct choice.