I have just finished some of my exercises and this sentence really make me confused:
Sometimes the symptoms are so slight you do not even know you have an allergy, and it may take years for an allergy to become noticeable.
I don't understand why there wasn't any conjunction between two clauses: 'Sometimes the symptoms are so slight' and 'you do not even know you have an allergy'.
Could anyone explain it to me, please?
There is a conjunction; it's just that it's been omitted—but still understood to exist:
Sometimes the symptoms are so slight [that] you do not even know you have an allergy.
It's common to omit the use of that in many constructions. Idiomatically, the two parts of the sentence are understood to have the relationship between each other made explicit by that.
In fact, some people adhere to the style of deliberately omitting that for the purpose of eliminating words that aren't essential for easy comprehension.
Why English speakers have all come to easily (in most cases) understand sentences without the use of that in particular is not something I could readily explain. Unfortunately, it may be another quirk of English that makes it more difficult for those learning the language.
