The easiest way to solve this question is to know the idiom:

While some x,
others y,
and still others z.

Where x, y, and z are reasonably parallel.

The initial sentence says:

While some propose...
others by suggesting...
still others by calling...

This is not a good choice. Our leading candidates are (C) and (E).

Many students pick (C) because it seems more parallel than (E). However, (C) contains a defect. It says "reducing software prices for decreasing" rather than "to decrease."

When we are stating our purpose, we should always say to+verb. For example:

I went to London to see Big Ben (not for seeing).
I studied at university to earn a degree (not for earning).
I saved money to buy a house (not for buying).

Answer choice (E), while not perfectly parallel, is a better answer.

This leads us to realize that parallelism is not a straitjacket that restricts our choices but rather a tool that we use to eliminate ambiguity and enhance the meaning and clarity of sentences. It is good to master parallelism, but we should never make parallelism our master.