The common side effect with fluoxetine therapy is -
Amongst the give options, option d i.e. is the best answer (read below).
Most common side effects on long-term treatment are sexual dysfunction. However, you should keep in mind that sexual dysfunction is the most common side effects on long-term use. Otherwise, nausea and GI disturbances are the most common side effects.

"Transient nausea is the most frequent complaint with the SSRIs".  
"The prominent side effects with SSRIs are gastrointestinal". 
The most frequent GI complaints are nausea, diarrhea, anorexia, flatulence, dyspepsia". 

The most common side effect of SSRIs is transient nausea.
If nausea is not given in options, then any other GI symptom (diarrhea, vomiting, anorexia) is the best answer.
The most common side effect of SSRIs on long-term use is sexual dysfunction.
Seizure
Anxiety
Hypotension
Loose stools