题干
Jack， American teacher，is arriving at our school by car.
A：a；the
B：an；不填
C：an；the
D：a；不填
答案(点此获取答案解析）
B
Jack， American teacher，is arriving at our school by car.
A：a；the
B：an；不填
C：an；the
D：a；不填
是正数等差数列，
是正数等比数列，且a1=b1，a2n+1=b2n+1，则
