Consider the following statements in relation to RNA interference (RNAi).

i. Double stranded RNA rather than single stranded antisense RNA is the interfering agent.

ii. RNAi is highly specific

iii. Only a few double stranded RNA molecules per cell are required for effective interference.

iv. The interfering activity is effective only in the cells and tissues adjacent to the site of introduction or expression.

Choose from the above the correct combination of features of RNA interference