A gerund is a verb form that ends in -ing and has the force of a noun and a verb.
A gerund may function as the subject or object of a verb, as a complement of a linking verb, or as the object of a preposition.
E.g. Reading is a good hobby.
Here Reading is a gerund and used as a noun. Also notice that Reading(noun) is the subject of the sentence. There is no action verb here. "is" is the linking verb whose complement is hobby.
Can you tell me which one is a Gerund and which one is a verb in the following sentences?
1. My favorite hobby is dancing.
2. My favorite niece is dancing.
A participle is a verb form that has the force of a verb and an adjective. While a present participle ends in –ing, a past participle ends in –ed,-d,-t,-en, or –n.
Shouting at the gate, John asked for help.
Here shouting is present participle which is introducing opening modifier. The opening modifier modifies the first noun after comma which is John in the example in hand.
Similarly participles, both present and past, can introduce middle modifiers, essential and non-essential, as well as end modifiers.
Now answer which one is a Gerund and which one is a participle:
A) A major part of the Secret Service's job is protecting the President.
B) We enjoyed visiting the new museum.
C) Lowering the interest rate can stimulate the economy.
D) The man sitting by the library door is waiting for his wife to finish her research.