I'm not sure that ...

[hirashin]

Hello, native English speakers,

(a) I'm not sure if mini skirts will be in fashion this summer.
(b) I'm not sure whether mini skirts will be in fashion this summer.
(c) I'm not sure that mini skirts will be in fashion this summer.

I think (a) and (b) would be all right, but how about (c)?
Would (c) also sound right?

Hirashin

 

[hirashin]

Addition:
(d) I'm not sure mini skirts will be in fashion this summer.

Thanks in advance.

Hirashin

 

[Lothor]

Addition:
(d) I'm not sure mini skirts will be in fashion this summer.

Thanks in advance.

Hirashin

All OK to me.

 

[hirashin]

Thanks, Lothor.

 

[mdchachi]

I agree. All are acceptable.

 

[hirashin]

Thanks, mdchachi.