In the equation above，k，r，s，t，and v represent positive numbers． Multiplying which one of these numbers by 2 will reduce the value of n to of its present value（）

单项选择题If y is a two—digit number with tens digit t and units digit M and the table above is a multiplication table for t and u (for example，t×u=6)，then y2=（）

A. a+2b+10c
B. 10a+20b+x
C. 10(a+2b+c)
D. 100(a+26+c)
E. 100a+20b+c

单项选择题If the value of the expression above is to be halved by doubling exactly one of the five numbers a，b，C，d，or e，which should be doubled（）

A. a
B. b
C. c
D. d
E. e