Answer:
The sentence that contains a split infinitive is:
* Young children seem to thoroughly enjoy playing with soap bubbles and shaving cream.
Step-by-step explanation:
A split infinitive is a grammatical structure where a word becomes between to and the main verb which would make a regular infinitive, there are several examples of infinitives among the sentences given but only one expression has a split infinitive "to thoroughly enjoy" the word "thoroughly" comes between the two elements that form the infinitive.