You ...... ( to be) sick if you eat that!
You are going to be sick if you eat that.
I think it .....( rain ) later so take an umbrella with you.
I think it will rain later so take an umbrella with you.
According to the weather forecast it ...... (to rain), so you'd better take an umbrella!
According to the weather forecast it is going to rain, so you'd better take an umbrella!