For the first question: By the time tennis practice is over, Mother will make dinner.
For the second: Four days of raining caused many cars to be completely submerged. I'l answer the question in Explaination.
Explanation:
The meaning of the word "submerged" as it is used in the sentence: The meaning is the cause to be under water, descend below the surface of an area of water & completely cover or obscure.