So the constant is π/6.

The test center of the problem is in the second half, pointing out that the exact value of pi should be calculated, so the constant can be changed to

Estimate the error of pi, that is, pi ~= 6/k

(A)π= 6 *(9/ 16)= 3.375

(B) pi = 6* ( 1/2) =3

(C)pi = 6 *( 157/300)= 3. 14

(D)pi = 6 *( 1 1/2 1)~ = 3. 142857

At first glance, C's answer is close, but compared with 3. 14 159, D's answer is more accurate.

Key points of quick answer: analyze concepts and formulas, extract key points of questions, convert them into computable formulas, and find out the answers with the least alternative answers before screening.

Test sites: ball volume, integer simplification (radius-diameter conversion), reciprocal conversion, accuracy judgment, cyclic decimal 1/7.

Non-test center: the issuer is purely a smoke bomb.