​
9
8
a
+
4
8
a
−
5
8
8
9
​
a+
8
4
​
a−
8
5
​

A
138a−58
8
13
​
a−
8
5
​

B
58a−58
8
5
​
a−
8
5
​

C
811a+14
11
8
​
a+
4
1
​

D
78a+85
8
7
​
a+
5
8
​