Water flows in streamline motion through a tube having a horizontal...

According to Bernoulli's theorem for a horizontal flow of an ideal fluid:

$P + \dfrac{1}{2}\rho v^2 = \text{constant}$

From the equation of continuity:

$A v = \text{constant}$

If the tube has a uniform cross-section, the area $A$ is constant, which means the velocity $v$ is constant throughout the tube. Therefore, the pressure $P$ is equal at all points. This makes the second option correct.

If the tube has a non-uniform cross-section, the velocity $v$ will vary. However, if the cross-sectional areas at points $A$ and $B$ are equal ($A_A = A_B$), the velocities at these two points will be equal ($v_A = v_B$). In this case, the pressures at $A$ and $B$ will be equal. This makes the first option correct.