What is true about the heterozygous sickle-cell (HbA HbS) condition?

Options:

sickle-cell anemia is not expressed

sickle-cell anemia is expressed under conditions of oxygen deficiency

sickle-cell anemia is apparent in men

none of the above

sickle-cell anemia is not expressed

Explanation:

The heterozygote conditions shows that, the manifestation of theses condition is only possible if the carrier man (HbSHbA) get married to another heterozygote woman, (another carrier) so that the two recessive alleles are expressed as SS.

But as AS, this is not possible because of the non defective A-allele which is always dominant over the S