In what way do the people actually disappear in the city is so big

behind closed elevator doors

Explanation:

In The City Is So Big poem,  things   were happening in an abnormal ways (strange manner). in stanza 3, machines eating houses and stairways were walking all by themselves and due to all these, people could not bear the ugly incidences happening again and to avoid further incidence they  disappear through the elevator doors.

answer; the correct answer to the above statement is to increase the production of milk in a herd of milk cows, the highest producing cows were chosen as the mother;

giant impact theory - the moon was formed from the collision between earth and another mars-sized body.

colliding planetesimals hypothesis - the moon was formed from the same cloud of material as earth.

capture hypothesis - the moon was locked into orbit by earths gravity as it was passing by it.

accretion hypothesis - the moon was formed from collisions and combining of planetesimals.

i think this is right, if not and you know better let me know.