All the statements can be used to explain about Earth's magnetic field.
Earth's magnetic field is almost same to that of the bar magnet. The magnetic field of the earth occurs from its core. It has an inner core which is solid in nature. in the outer core, there is a motion of the liquid due to heat flow from the inner core to the core mantle boundary which proves that the outer core is liquid and moving. The Earth's core consists of iron and nickel as the Eddy currents in the iron and nickel liquid helps generating the Earth's magnetic field.
Hence, all the three statements are true and can be used to explain the Earth's magnetic field.
the answer is b) magnetic current
I believe the answer is C
First we will find the speed of the ball just before it will hit the floor
so in order to find the speed of the cart we will first use energy conservation



So by solving above equation we will have

now in order to find the momentum we can use



Answer:
(A). The flux is 0.336 N.m²/C
(B). The flux is zero.
Explanation:
Given that,
Length = 4.2 cm
Width = 4.0 cm
Electric field 
Area vector is perpendicular to xy plane
(A). We need to calculate the flux
Using formula of flux

Where, E = electric field
A = area
Put the value into the formula



(B). Given electric field

We need to calculate the flux
Using formula of flux

Put the value into the formula

Here, The component of k is not given
So, the flux is

Hence, (A). The flux is -0.336 N.m²/C
(B). The flux is zero.