Hi guys

I need your help with this exercise.
1 - Change this sentence to the Imperative form: "We don't tell her about our plans"
The correct alternative is:
a) We don't tell her about our plans (this means that the sentence above does not have an imperative, I guess)
b) Let's don't tell her about our plans
c) Let's not tell her about our plans
Which is the correct alternative? I marked C, am i right?
Thank you guys

xxThaisLima