— He got to Guangzhou ________ the morning of the 16th of April.
A:at; in
B:in; in
C:to; on
D:in; on
①A→C运动是匀速运动; ②B→D运动是匀速运动;
③A→C平均速度为3a/2△t;④通过D点时速度为a/△t.
设a,b,c为正数,求证:a2b+b2c+b2a≥a+b+c ..