It depends where you take time= zero to be.
If you take time is zero at zero displacement, then at this point the acceleration is also zero. You would get a (negative) sine wave. (Value zero at t=0)
In the mark scheme it says negative sine wave, but there is no indication in the question that we are suppose to take zero displacement to be t=0. Would we have to indicate in the graph that we have taken the initial displacement to be t=0?
It does no harm to state this.
However, it's generally accepted, unless otherwise started, that the original displacement time graph for SHM is a sine wave.
If this is the case, then the acceleration time graph is a negative sine wave and the velocity time graph is a cosine wave.