SaveDefinitions is an option to Manipulate and related functions that specifies whether current definitions relevant for the evaluation of the expression being manipulated ...

ShrinkingDelay is an option for dynamic objects that specifies how long to delay before shrinking the size of the region in which the object is displayed to the actual size ...

SignPadding is an option for NumberForm and related functions that specifies whether padding should be inserted after signs.

SynchronousInitialization is an option for Manipulate, DynamicModule, and related functions that specifies whether or not to evaluate the expression given as the setting for ...

TraceOriginal is an option for Trace and related functions which specifies whether to test the form of each expression before its head and arguments are evaluated.

VerifyConvergence is an option to Sum, NSum, and similar functions that specifies whether convergence checking should be done.

ViewRange is an option for Graphics3D and related functions which specifies the range of distances from the view point to be included in displaying a three-dimensional scene.

WordSeparators is an option for Read, Find, and related functions that specifies the list of strings to be taken as delimiters for words.

$ControlActiveSetting is a symbol whose value is True if it is evaluated while a control is active, or in certain other previewing situations.

You can enter complex numbers in Mathematica just by including the constant I, equal to Sqrt[-1]. Make sure that you type a capital I. If you are using notebooks, you can ...