Hint: Beautiful is an adjective, which means, pleasing the senses or mind aesthetically.
Complete answer:Beautiful is generally referred to as being of a very high standard; excellent. The definition of beautiful is, full of beauty; possessing qualities that delight the senses, especially the eye or the ear, or awaken admiration or approval in the mind. For example; She writes beautiful poetry.
Now, we will examine all the options and find the correct answer to the given question :
Option 'a' is Ugly. Ugly is a state of being unpleasant/unsightly or repulsive, especially in appearance. Ugly can also be referred to as something that is offensive to the sight; hideous. For example; People said that I was ugly back then.
Option 'b' is Dark. Dark means something with little or no light. It can also be interpreted for colour or object, as something not reflecting much light or approaching black in shade. For example; It's too dark to see much.
Option 'c' is Rough. Rough means something that has an irregular or uneven surface; not smooth or level. For example; The road was very rough.
Option 'd' is Dirty. Dirty means something covered or marked with an unclear substance. It can also be interpreted as someone who is dishonest or dishonorable. For example- He had a reputation for dirty dealings.
Now as we know the meaning of all the options, we can clearly make out the correct answer. The opposite of beautiful is ugly.
Note: The word ugly has several meanings. It can be used to describe something displeasing or a mood of anger or a bad feeling, as well.
