Foreign institutional investors (FIIs) were net buyers of Rs 375.78 crore in the futures & options (F&O) segment on Thursday.According to data released by NSE, FIIs were net buyers of index futures of Rs 72.22 crore and index options of Rs 163.18 crore.They were net buyers of stock futures of Rs 134.46 crore and sold stock options worth Rs 5.92 crore.