Martha believes that if she doesn't keep checking the stove in the kitchen, a gas leakage may occur and may cause an explosion. consequently, martha keeps checking whether the stove has been turned off over and over again, sometimes over fifty times a day. this practice interferes with her sleep and disturbs her thoughts. in the context of anxiety and anxiety-related disorders, martha's recurrent thoughts about the possibility of an explosion are called

This recorrent thought about an iminent explosion because of a gas leaking is a symptom of an Obsessive-Compulsive Disorder (OCD). The Obsessive-Compulsive Disorder is one of the five major types of anxiety disorders, the others are Generalized Anxiety Disorder, Panic Disorder, Post-Traumatic Stress Disorder and Social Phobia.

The OCD is characterized by recurrent unwanted thoughts, in other words, obsessions, which causes the person to have repetitive behaviors  such as checking whether the stove has been turned off or not over and over again. This repetitive behavior is done in a false hope of making the obsession dissapear, that is, Martha checks the stove hoping this compulsion will dissapear after she sees that there is no gas leaking. However, that relief is temporary and she ends up repeating the behavior indefinetely.

a. the moon was locked into orbit by the earths gravity as it was passing by and capture hypothesis i think