[X was the first thing that happened.] = Several things happened, but X happened before all the others.
[The woman had her first child two years after she married, and then she had another child three years after that.]
11-24. explain, explains, to explain, explaining, explained.
[X explains something.] = X carefully tells you something you did not know about a thing, or what something means, or what caused something to happen.
[I will show you the parts of this machine and explain what each part does.]
[I can explain what caused these plants to die.]
[J was caused by K.] = K caused J.
[The food was eaten by the children.]
11-26. lesson, lessons.
[X is a lesson.] = X is something that someone plans and does at a time to help people learn something.
[My school gives me a reading lesson each day.]
[Maybe you can learn to play music, if someone gives you lessons.]
Someone needs to explain what happened here.
Maybe the building __________.