Answer : A
How answer A is True ?
If you consider this CFG you can definitely generate odd no of a's and odd no of b's no one going to stop you but the real question can you generate all the strings out of this grammar which are having odd no of a's and odd no of b's Answer is no you can't generate.
Consider option B : The string in which you have abbb (odd no of a's and odd no of b's ).This string can't be generate by this grammar you can try it .We only consider the Language if it is able to generate all the possible strings of that type .
Consider the option C : here again you can generate the strings having odd no of a's and even no of b's but you can't generate all .One of the string which you can't generate is " a" (Here we have 1-a and 0 no of b's) .
consider the option D :here again we are able to generate some of the string which are having even no of a's and even no of b's .But not all Here is the Exp : we can't generate epsilon in which we have even no of a's and even no of b's .
Finally Consider option A in this you can generate all possible string out of this grammar in which you are going to have equal no of a's and equal no of b's .
That's why option A is correct .