Answer: Option B
Let the number of Rose plants be a.
Let number of marigold plants be b.
Let the number of Sunflower plants be c.
According to question,
20a + 5b + 1c = 1000 - - - - - - (1)
a + b + c = 100 - - - - - - - - - - (2)
Solving the above two equations by eliminating c,
19a + 4b = 900
b = $$\frac{{900 - 19a}}{4}$$   = $$225 - \frac{{19a}}{4}$$   - - - - - - - (3)
b being the number of plants, is a positive integer, and is less than 99, as each of the other two types have at least one plant in the combination i.e .
0 < b < 99 - - - - - - - (4)
Substituting (3) in (4),
0 < 225 - $$\frac{{19a}}{4}$$ < 99
⇒ 225 < -$$\frac{{19a}}{4}$$ < (99 - 225)
⇒ 4 × 225 > 19a > 126 × 4
⇒ $$\frac{{900}}{{19}}$$ > a > 504
a is the integer between 47 and 27 - - - - - - - - (5)
From (3), it is clear, a should be multiple of 4.
Hence, possible values of a are (28,32,36,40,44)
For a=28 and 32, a+b>100
For all other values of a, we get the desired solution:
a=36,b=54,c=10
a=40,b=35,c=25
a=44,b=16,c=40
Three solutions are possible.