_______hard you try, it is difficult to lose weight without cutting down the amount you eat .

A．However

B．Whatever

C．Whichever

D．Whenever

市售浓硫酸中溶质的质量分数98%，密度为1.84 g·cm^-3。计算市售浓硫酸中H₂SO₄的物质的量浓度。