The nurse receives telephone messages from the following 4 clients. Which client should the nurse call back first?
选项：

A:

Client taking cyclosporine who reports swollen and bleeding gums for several days

B:

Client taking doxycycline who reports severe sunburn after sun exposure

C:

Client taking phenytoin who reports flu-like symptoms and a new painful skin rash

D:

Client taking sildenafil who reports dizziness when standing up from a seated position