The correct answer is: C. Either I or II is implicit
The statement “His recent investment in the shares of Company A is only a gamble” means that there is a high degree of uncertainty about the outcome of the investment. It is possible that he will make a profit, but it is also possible that he will lose money.
Assumption I is that he may incur loss on his investment. This is a logical assumption, because any investment carries the risk of loss.
Assumption II is that he may gain from his investment. This is also a logical assumption, because any investment also carries the potential for profit.
Neither assumption is explicitly stated in the statement, but both are implicit in the nature of a gamble. Therefore, the answer is C.