ask my dearest teachers' help

I need you help,teachers. Would you like to explain them?
1. We deal in decorative fabrics_________ different varieties.
A on B. of C. in D. for
2. As agreed upon in our negotiations, payment_____ L/C.
A. by B. is by C. will be D. will by
3.The 505 Vital Herb pad, our new product, is based on a ___ concept.
A.traditional B. newest C. old D. excellent
4. Our offer ________ firm till August 31.
A. could be B. for C. will be D. is to

[Casiopea]

We try not to do homework assignments for you, but if you provide your answers first, we'd be more than willing to help you out.