Answer: A. silicon and oxygen
Step-by-step explanation:
The two most abundance elements in earth's crust are silicon and oxygen.
The most abundant element in earth's crust is Oxygen (O) which has a percentage composition of 46.6%. Oxygen is mainly present as silicates, carbonates, sulphates etc.
The second most abundant element in earth's crust is Silicon (Si) which has a percentage composition of 27.7% . Silicon is present in the form of silicates.
The third most abundant element in earth's crust is aluminium (Al) which has a percentage composition of 8.1 %.
The fourth most abundant element in earth's crust is Iron (Fe) which has a percentage composition of 5.0 %.