Step 1: Understand the topic:
The chapter on power sharing lists four forms of sharing power: between organs of government, between governments at different levels, between social groups, and between political parties, pressure groups and movements.
This question is about the fourth form.
Step 2: Check the Assertion (A):
In a democracy, parties compete for power, so the party in power can lose it in the next election. This competition keeps a check on those who rule.
Pressure groups such as trade unions, farmers' associations and business bodies, and movements such as the Narmada Bachao Andolan, also influence decisions of those in power.
So Assertion (A) is TRUE.
Step 3: Check the Reason (R):
The main idea of power sharing is that power should not stay with one person or one group. When many groups can control or influence the rulers, power is spread out.
So Reason (R) is TRUE.
Step 4: Link the Reason to the Assertion:
Control by parties, pressure groups and movements counts as power sharing exactly because it stops power from remaining in one hand.
So (R) is the correct explanation of (A).
Step 5: Why the other options are wrong:
Option B accepts both statements as true but says (R) does not explain (A). This is wrong, because the Reason states the very purpose of the arrangement in the Assertion.
Option C says (R) is false. This is wrong, because spreading power is the basic aim of power sharing.
Option D says (A) is false. This is wrong, because NCERT clearly lists this as a form of power sharing.
Final Answer:
Both statements are true and the Reason explains the Assertion. The correct choice is option A.
\[ \boxed{\text{Option A}} \]