Select the most appropriate option to fill in blank number 5.

Correct — B. The window is "the subsequent four months", so the average must be struck often enough to give several readings inside it. A monthly average gives four, which is enough for a downtrend to show.

The passage counts in months throughout — during the past three months, in the subsequent four months — so the series it reports is a monthly one.

Option (b) is the key.

Why the others are wrong

• (a)
  yearly — Yearly gives one figure a year, and four months contain no full year and no second figure to compare. A single number cannot show a downtrend.
• (c)
  half yearly — Half yearly gives two figures a year, so a four-month window holds at most one of them. Again there is nothing for the price to trend against.
• (d)
  weekly — Weekly averages would fit four months arithmetically, but the passage measures time in months at every other point and never in weeks, so weekly breaks the frame the paragraph sets.

The last blank is a unit-of-measure blank, settled by arithmetic plus the passage's own habit.

Arithmetic first: a trend needs at least two points. Inside four months a yearly average yields one point at most and a half-yearly average one, so neither can show anything.

The paragraph's habit second: it measures in months — three months, then four months — and never in weeks, so monthly keeps the passage consistent.

Key facts

• A trend needs at least two data points, so the averaging period must be shorter than the window described.
• This passage states time only in years and months, never in weeks.
• A monthly average across four months gives four readings.

Common traps

• Choosing weekly because it also fits four months, without checking which unit the passage uses.
• Treating the blank as a vocabulary test when it is really a consistency test.

No directly related past PYQ was found.