None of those answers are suitable to me.
Government bonds are generally regarded as low-risk and they typically have modest (low) interest rates for return on investment, and these are advantages really. So we can discount answer A, C, and D.
I guess you could say that bonds can be hard to find (Answer B) but this not really true. There is always a bond market to trade bonds on. It requires setting up a trading account or speaking to a broker so this can be more difficult than putting money in a bank account, but to be honest I don't think any of those answers are appropriate for the question.
