Answer:
A. My aunt and uncle usually sends me a picture postcard when they travel.
Step-by-step explanation:
The subject is My aunt and uncle. This phrase can be replaced with the pronoun they because we have two people here who send me a postcard. So the verb number needs to be changed in order to agree with the number of the subject: it should be send, not sends.
In other words, use a plural verb with two or more subjects when they are connected by and.