What is the feature ofuterine contractionsin threatened labor

A.The contraction usually lasts ≥ 30 seconds , with a break of 5-6 minutes

B.The contraction usually lasts ≥ 15 seconds , with a break of 3-5minutes

C.The contraction usually lasts ≥ 40 seconds , with a break of 3-4 minutes

D.The contraction usually lasts ≥ 15 seconds , with a break of 3-4 minutes

正确答案：The contraction usually lasts ≥ 30 seconds , with a break of 5-6 minutes