An Experiment Consists of Three Tosses of a Two-Sided Coin

Multiple Choice

An experiment consists of three tosses of a two-sided coin with the possible outcomes heads (H) or tails (T) from each toss.The outcome space is: ​
S = {HHH, HHT, HTH, THH, HTT, THT, TTH, TTT}
​
We define event A as "no heads are observed" and event B as "no tails are observed." What is AUB?

A) { } (the empty set)
B) {HHH}
C) {TTT, HHH}
D) {TTT}