Comprehension:

In the following passage some of the words have been deleted. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

The thought here is that because saliva is (1) ________ alkaline, stimulating it by chewing gum after eating (2)_____ help neutralize the acidity in your mouth and throat. (3)______ a very small study from 2005 did (4)_______ some merit to this approach, the size of the study makes it difficult to (5)_______ any real conclusions.

Select the most appropriate option to fill in blank number 1.

slightly 

- The word 'slightly' is the most suitable for the blank.

The complete sentence is : 

The thought here is that because saliva is slightly alkaline, stimulating it by chewing gum.

- The word "slightly" appropriately fills the blank. It indicates that saliva is somewhat or to a small degree alkaline. The context suggests that the alkalinity of saliva is not extremely high but rather mildly or slightly alkaline.