设曲线y=xⁿ⁺¹（n∈N*）在点（1，1）处的切线与x轴的交点的横坐标为x_n，令a_n=lgx_n，则a₁+a₂+…+a₉₉的值为（    ）。

According to the speaker, the proportion of college students with loans in the United States has increased from 50% in 1993 to about 67% at present and the average loan debt when they graduate is 17,000 dollars.