<p>Flowering plants, which brighten streets and delight children and</p>
<p>adults with their beauty, plays a crucial role in the environmental</p>
<p>infrastructure of many cities. No error</p>
<p>Flowering plants … PLAY a crucial role.
The trick here is to “cross out” the clauses.</p>
<p>For the second one, “more wider” is ungrammatical.</p>
<p>I thought Gerunds would be singular? ie. Constructing new skyscrapers often takes many months</p>
<p>In this case, “flowering” is an adjective and describes the plants. Therefore, the subject is actually “plants” and therefore is plural.</p>