The Korotkoff sound is the one item that cannot be mistaken — it belongs to blood pressure — and only option 3 places it there. The code is a-ii, b-i, c-iv, d-iii.

a — the Miller sweep. A CRO's horizontal deflection must be a linear ramp, or the time axis is distorted. Charging a capacitor through a resistor gives an exponential, not a ramp. The Miller circuit puts the capacitor in the feedback path of a high-gain inverting amplifier — that is, makes it an integrator — so the capacitor charges from a virtual earth at constant current and the output falls linearly:

\(V_{o}=-\dfrac{1}{RC}\int V_{i}\,dt=-\dfrac{V_{i}t}{RC}\)

The name comes from the Miller effect, which multiplies the capacitance by the amplifier's gain.

b — why transients need storage. A conventional oscilloscope displays a repetitive waveform because the trace is redrawn many times a second and persistence does the rest. A transient occurs once: the trace flashes and is gone before the eye can follow it. A storage oscilloscope — originally with a bistable storage mesh in the CRT, now by digitising into memory — captures the single event and holds it for examination.

c — Korotkoff sounds. These are the sounds heard through a stethoscope over the brachial artery as a cuff is deflated. The pressure at which they begin is the systolic reading; the pressure at which they disappear is the diastolic. They arise from turbulent flow through the partially occluded artery, and automated blood-pressure monitors detect the same phenomenon with a microphone or by oscillometry.

d — Lissajous figures. Feed one sinusoid to the vertical plates and another to the horizontal, and the spot traces a closed figure whose shape depends on the frequency ratio and the phase difference. For equal frequencies the figure is an ellipse, and

\(\sin\phi=\dfrac{y_{1}}{y_{2}}\)

where \(y_{1}\) is the y-intercept and \(y_{2}\) the maximum — a straight line at 0° or 180°, a circle at 90°. For unequal frequencies the ratio of tangent points on the two axes gives the frequency ratio.

Hence, the correct code is a-ii, b-i, c-iv, d-iii.