Swine Flu - Vocabulary Matching

Match each pair, and then click the Check button.
1 apparent
2 approximate
3 classical
4 constant
5 contact
6 detect
7 document
8 duration
9 emerge
10 environment
11evidence
12 exhibit
13 exposure
14 factor
15 identify
16 internal
17 isolate
18 license
19 occur
20 previously
21 similar
22 source
23 transmit
24 variation
25 widespread