单选题 19. If oven cleaner is added to household bleach, the mixture emits chlorine gas. A mixture of bathtub cleaner and household bleach also emits chlorine gas. If ordinary soap is added to household bleach, no gases are emitted. When an unidentified cleaning agent was added to household bleach, no chlorine gas was emitted.
If the statements above are all true, which of the following can be determined conclusively on the basis of them about the unidentified cleaning agent? ______

A、 It was ordinary soap.
B、 It was either oven cleaner or bathtub cleanser.
C、 It was neither oven cleaner nor bathtub cleanser.
D、 It contained ordinary soap and either oven cleaner or bathtub cleanser.
E、 It contained ordinary soap and neither oven cleaner nor bathtub cleanser.

【正确答案】 C

【答案解析】 C：该选项与文章结论一致，正确。
A：未知清洁剂不一定就是普通肥皂，不选。
B：如果是烤箱清洁剂或浴缸清洁剂，那么与家用漂白剂混合后会产生氯气，与原文矛盾，不选。
D：不能包含烤箱清洁剂或浴缸清洁剂，不选。
E：一定需要包含普通肥皂，不选。