A couple of questions about using articles

[eureka1]

Hi,

I'd be grateful if someone would tell me which of the following is grammatically correct and WHY:

(1) Negotiations between the countries has reached a crucial stage vs THE negotiations between the countries has reached a crucial stage.
(2) The drug boosts THE immune system vs The drug boosts immune system.
(3) THE security around the city.... vs security around the city...

Thanks

[billmcd]

Hi,

I'd be grateful if someone would tell me which of the following is grammatically correct and WHY:

(1) Negotiations (might not have been specifically identified previously) between the countries has reached a crucial stage vs THE negotiations (probably referred to previously) between the countries has reached a crucial stage.
(2) The drug boosts (a specific drug) THE immune system (as opposed to other systems) vs The drug boosts immune system. (must use the article in this context/statement)
(3) THE security (referred to previously) around the city.... vs security (in general) around the city... e.g. "Security around the city has been reinforced with additional forces. The security includes military and civilian personnel."

Thanks

b.

[emsr2d2]

The negotiations have ​reached a crucial stage ...