Exercise 1: Why Substitutes and Time Both Push Elasticity the Same Direction — Possible Solution
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Both factors, despite being genuinely different in nature, work by
affecting the same underlying thing: how many REAL, PRACTICAL options a
buyer actually has available for responding to a price increase
instead of simply paying it.

Substitute availability directly determines the RANGE of real options
at any given moment - if a close substitute exists, a buyer has an
immediate alternative to switch to the moment a price rises, without
needing any extra time to create that option. More substitutes means
more real ways to avoid paying the higher price right away.

Time horizon works differently but points toward the exact same kind
of outcome: even a good with genuinely few substitutes AT THIS MOMENT
can gain real new ones over time - a driver can't switch away from
needing petrol today, but given years, they can genuinely create a
new option that didn't exist for them before (a fuel-efficient
vehicle, a shorter commute, access to public transit). Time doesn't
directly reduce necessity, but it lets buyers build or discover
substitutes that weren't practically available in the short run.

Because both factors ultimately increase the real number of practical
alternatives available to a buyer - one by adding options that already
exist, the other by giving buyers time to create or find new ones -
both push elasticity in the same direction: toward MORE elastic
demand, since more available alternatives always make it easier for
buyers to respond to a price increase by switching rather than simply
paying more.

ANSWER: Both factors increase the real number of practical
alternatives available to a buyer facing a price increase - substitute
availability provides options that already exist right now, while a
longer time horizon lets buyers create or discover new options they
didn't have in the short run. Since more available alternatives always
make demand more elastic, both factors push in the same direction even
though they operate through different mechanisms.

WHY THIS WORKS AS AN ANSWER
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This identifies the shared underlying mechanism (available practical
alternatives) connecting two genuinely different-sounding factors,
rather than simply asserting both happen to increase elasticity.