What is the feature ofuterine contractionsin threatened labor

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