The Activity of a Radioactive Sample Is the Number of Decay

The activity of a radioactive sample is the number of decay events per second. The SI unit of activity is the becquerel (1 Bq = 1/s) . An older unit for activity is the curie (1 Ci = 3.70 $\times$ 10¹⁰/s) . What is the activity in $\mu$ Ci of a sample with an activity of 2.1 10 ⁵ Bq of radiation?

A) 7.8 $\times$ 10 ⁹ $\mu$ Ci
B) 5.7 $\mu$ Ci
C) 5.7 $\times$ 10 ^-12 $\mu$ Ci
D) 5.7 $\times$ 10 ^-6 $\mu$ Ci
E) 0.21 $\mu$ Ci