Concept:The connector must join two positive ideas about friendship by showing addition.
Explanation:The first sentence says people with good friends recover faster from illnesses and surgeries.
The second sentence says friendships protect individuals from physical and mental health problems.
Both sentences highlight the benefits of friendship in a positive way.
Therefore, the connector should add one benefit to another without changing the meaning.
"In addition to this" is used to add a related positive point, so it is correct.
"Furthermore" also introduces additional supporting information, so it is correct.
"To make matters worse" indicates a negative or worsening situation, which does not fit here.
Thus, connectors 1 and 3 can be used to form a single coherent sentence.
Example: "People with good friends recover more quickly from illnesses and surgeries; in addition to this, friendships can protect individuals from physical and mental health problems."
Equivalent sentence with "furthermore" also works.
Answer:Both 1 and 3
Therefore, the correct option is C.