A, washing with water can only dilute concentrated sulfuric acid, and cannot remove the harm of sulfuric acid, so the option is wrong;

B, solid alkali can react with sulfuric acid, can consume sulfuric acid, will not generate harmful substances, so the option is correct;

C, directly covering sulfuric acid with sand cannot consume and eliminate the harm of sulfuric acid, so the option is wrong;

D, directly diluting with water and reusing alkaline substance A will release a lot of heat, which is more dangerous, so the option is wrong;

So choose B.