To answer this question, you need to understand idioms related to relationships and marriages. Let's go through each option to understand why it is correct or incorrect:
Option A) "getting serious" - This option is incorrect because it means that a relationship is becoming more committed and intense, but it does not imply that there are problems or difficulties.
Option B) "on the rocks" - This option is correct because it is an idiom that means a relationship or marriage is experiencing difficulties or problems.
Option C) "a match made in heaven" - This option is incorrect because it means that a couple is well-suited for each other and their marriage is perfect and harmonious, which contradicts the statement about experiencing problems.
Option D) "puppy love" - This option is incorrect because it refers to a young and immature love, typically experienced by teenagers, and does not convey the idea of a marriage experiencing problems.
The correct answer is B) "on the rocks". This option is correct because it accurately describes a marriage that is experiencing difficulties or problems.