数列{a_n}的前n项和为S_n，数列{b_n}的前n项的和为T_n，{b_n}为等差数列且各项均为正数，a₁=1，a_n+1=2S_n+1（n∈N⁺），b₁+b₂+b₃=

15．

（1）求证：数列{a_n}是等比数列；

（2）若a₁+b₁，a₂+b₂，a₃+b₃成等比数列，求T_n．

—______is the Changjiang river in China, do you know?

—Yes, it’s about 6,380 kilometers long.

A．How many

B．How wide

C．How long

D．How much