Following is a requirement from section $7\mathrm{.}7\mathrm{.}2$ of the Mars Polar Lander requirements The touchdown sensors shall be sampled at $100-$ Hz rate $.$ The sampling process shall be initiated prior to lander entry to keep processor demand constant $.$ However $,$ the use of the touchdown sensor data shall not begin until $12$ meters above the surface $.($ Note : The altitude was later changed from $12$ meters to $40$ meters above the surface $."$ a $)$ it is not atomic b $)$ it is not verifiable $)$ it is incomplete $)$ it is ambigous