1. The resistor is located at point D.
A resistor is an element of a circuit that opposes to the flow of current through it: the value of its resistance (R) tells how much the resistor opposes to the flow of current, and the resistance is related to the voltage in the circuit (V) and the current (I) by the Ohm's law:

Resistance is measured in Ohm (
), and a resistor is usually represented with a zig-zag line as the one at point D.
2. The switch is located at point B.
A switch is an element of the circuit that can be switched on and off, opening and closing the circuit, therefore allowing or not the flow of current through it. When the switch is open, no current flows; when it is closed, the current can flow through the circuit.
The symbol of a switch is represented at point B.
The sunlight of all colors passes through air, the blue part causes charged particles to oscillate faster than does the red part. More of the sunlight entering the atmosphere is blue than violet, however, and our eyes are somewhat more sensitive to blue light than to violet light, so the sky appears blue.
Accuracy is a general concept while precision is more of a mathematical concept.