A laboratory requires a 32P source that will have an activity of 3.7GBq exactly 28days from now. The half-life of 32P is 14days and its atomic mass is 32g mol−1. The mass of 32P that must be prepared today is closest to ____.
a) 0.69μg
b) 0.34μg
c) 1.4μg
d) 0.14μg